Clean-up secure jobs config

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Describe in detail what your merge request does and why.

• allow_failure: true is redefined for every job, but it's a the default already for all secure jobs in their respective templates. I couldn't find anything in the config that could set this to false by default, so I think we can safely get rid of it.
• The gemnasium-maven-dependency_scanning is triggered on master, even though we don't have anything "java". The job fails silently.
• The workaround for the execa vulnerability should be needed anymore, I don't see this vulnerability in https://gitlab.com/gitlab-org/gitlab/-/pipelines/387803884/?reportType=DEPENDENCY_SCANNING.

Some open questions too:

• Why do we need to keep a GIT_DEPTH of 20? (example in this job: Fetching changes with git depth set to 20...). Shouldn't we keep that under 10 (at least for the secure jobs) according to https://docs.gitlab.com/ee/ci/large_repositories/index.html#shallow-cloning?
• Pipelines are reporting multiple vulnerabilities, but nothing ends up in the Vulnerability Report.
  • https://gitlab.com/gitlab-org/gitlab/-/pipelines/387803884/?reportType=DEPENDENCY_SCANNING&reportType=SAST has 79 Detected Dependency Scanning vulnerabilities, whereas https://gitlab.com/gitlab-org/gitlab/-/security/vulnerability_report/?scanner=GitLab.DEPENDENCY_SCANNING has only 1
  • There's a package-and-qa job always failing in these pipelines, I wonder if it could prevent the parsing of the reports. If it's the case, this a very weak condition, and we should fix that.

@rymai could you please take a look? thanks

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