Container scanner image 6.6.0 is failing to get relative path
### Summary
One of our [customers](https://gitlab.zendesk.com/agent/tickets/483185) (internal) reported that container scanning is no longer working. The main error is:
```
[ERROR] [2023-12-21 07:43:05 +0000] [container-scanning] > different prefix: "" and "/builds/SNIPPED/SNIPPED"
[ERROR] [2023-12-21 07:43:05 +0000] [container-scanning] > /usr/local/lib/ruby/3.1.0/pathname.rb:528:in `relative_path_from'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/remediation.rb:112:in `diff_to_patch'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/remediation.rb:104:in `create_patch'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/remediation.rb:79:in `to_hash'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/collection.rb:19:in `map'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/collection.rb:19:in `to_hash'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/converter.rb:40:in `convert'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/plugin/container_scan.rb:10:in `convert'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/scan.rb:26:in `scan_image'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/cli.rb:16:in `block in scan'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/cli.rb:15:in `map'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/cli.rb:15:in `scan'
/usr/local/bundle/gems/thor-1.3.0/lib/thor/command.rb:28:in `run'
/usr/local/bundle/gems/thor-1.3.0/lib/thor/invocation.rb:127:in `invoke_command'
/usr/local/bundle/gems/thor-1.3.0/lib/thor.rb:527:in `dispatch'
/usr/local/bundle/gems/thor-1.3.0/lib/thor/base.rb:584:in `start'
/usr/local/bundle/gems/gcs-6.6.0/exe/gtcs:14:in `<top (required)>'
/usr/local/bundle/bin/gtcs:25:in `load'
/usr/local/bundle/bin/gtcs:25:in `<main>'
```
From the stacktrace, it appears this might have been introduced here: https://gitlab.com/gitlab-org/security-products/analyzers/container-scanning/-/merge_requests/2944
When we set the image back to use `6.5.1`, scan succeeds.
### Steps to reproduce
See thread https://gitlab.com/gitlab-org/security-products/analyzers/container-scanning/-/merge_requests/2964?commit_id=62d6a504f18d49430bc75bfdf3f0c44c11b5bc15#note_1710640622
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### Example Project
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behavior, and link to it here in the bug report. If you are using an older version of GitLab, this
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### What is the current *bug* behavior?
Scan fails with an error.
### What is the expected *correct* behavior?
Scan succeeds.
### Relevant logs and/or screenshots
```
[ERROR] [2023-12-21 07:43:05 +0000] [container-scanning] > different prefix: "" and "/builds/SNIPPED/SNIPPED"
[ERROR] [2023-12-21 07:43:05 +0000] [container-scanning] > /usr/local/lib/ruby/3.1.0/pathname.rb:528:in `relative_path_from'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/remediation.rb:112:in `diff_to_patch'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/remediation.rb:104:in `create_patch'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/remediation.rb:79:in `to_hash'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/collection.rb:19:in `map'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/collection.rb:19:in `to_hash'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/converter.rb:40:in `convert'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/plugin/container_scan.rb:10:in `convert'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/scan.rb:26:in `scan_image'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/cli.rb:16:in `block in scan'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/cli.rb:15:in `map'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/cli.rb:15:in `scan'
/usr/local/bundle/gems/thor-1.3.0/lib/thor/command.rb:28:in `run'
/usr/local/bundle/gems/thor-1.3.0/lib/thor/invocation.rb:127:in `invoke_command'
/usr/local/bundle/gems/thor-1.3.0/lib/thor.rb:527:in `dispatch'
/usr/local/bundle/gems/thor-1.3.0/lib/thor/base.rb:584:in `start'
/usr/local/bundle/gems/gcs-6.6.0/exe/gtcs:14:in `<top (required)>'
/usr/local/bundle/bin/gtcs:25:in `load'
/usr/local/bundle/bin/gtcs:25:in `<main>'
```
### Output of checks
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#### Results of GitLab environment info
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<pre>
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#### Results of GitLab application Check
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<summary>Expand for output related to the GitLab application check</summary>
<pre>
(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:check SANITIZE=true`)
(For installations from source run and paste the output of:
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(we will only investigate if the tests are passing)
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### Possible fixes
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issue