Ignore .test files for CodeQL analysis.

Currently we run CodeQL analysis on the extension repository to spot potentially harmful patterns, and mistakes. This can lead to false positives on test cases where we might purposefully test a bad case. We should disable at least some, if not all, checks on test cases.

Start by locating the extension repository's CodeQL analysis workflow and configuration, then check how test files are identified. Adjust the analysis scope for .test files and run CodeQL to verify that test cases are excluded while the remaining analysis still completes successfully.

Written by the indexing model from the issue text.