Fix test for tags

What does this MR do?

Fix shell test in Secret Detection. There's no operand in the first test, so it will fail every time. The second one seems to have issues as well:

$ if [[ $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH ]]; then echo "Running Secret Detection on default branch."; /analyzer run; exit 0; fi
sh: master: unknown operand

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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• [-] I have self-reviewed this MR per code review guidelines.
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Availability and Testing

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Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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