Remove uopz PHP extension and refactor guard tests

[officialasishkumar]

Summary

Addresses issue:

• Remove use of uopz extension in tests #12332

Relevant technical choices

CI workflows: Removed uopz from the PHP extension lists in both php-lint-tests.yml and gemini.yml. No tests depend on it after this change.

Test refactoring (Tag_Environment_Type_GuardTest): Replaced all uopz_set_static calls with filter-based assertions using the existing googlesitekit_allowed_tag_environment_types filter:

• test_can_not_activate_when_environment_not_allowed: Filters allowed environments to exclude the current environment type, then asserts the guard rejects activation.
• test_can_activate_when_environment_is_allowed: Filters allowed environments to include only the current environment type, then asserts the guard permits activation.

This approach tests the same guard logic without requiring any additional PHP extensions. A tear_down method clears the filter between tests to prevent leakage.

The two existing pre-5.5 / post-5.5 WP version tests are preserved unchanged.

PR Author Checklist

• My code is tested and passes existing unit tests.
• My code has an appropriate set of unit tests which all pass.
• My code is backward-compatible with WordPress 5.2 and PHP 7.4.
• My code follows the WordPress coding standards.
• My code has proper inline documentation.
• I have added a QA Brief on the issue linked above.
• I have signed the Contributor License Agreement (see https://cla.developers.google.com/).

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Code Reviewer Checklist

• Run the code.
• Ensure the acceptance criteria are satisfied.
• Reassess the implementation with the IB.
• Ensure no unrelated changes are included.
• Ensure CI checks pass.
• Check Storybook where applicable.
• Ensure there is a QA Brief.
• Ensure there are no unexpected significant changes to file sizes.

Merge Reviewer Checklist

• Ensure the PR has the correct target branch.
• Double-check that the PR is okay to be merged.
• Ensure the corresponding issue has a ZenHub release assigned.
• Add a changelog message to the issue.