Fix path filtering in ci_linux_x86_clang_asan.yml.

[ScottTodd]

This ASan job should be running on every PR and push that affects the compiler code, but it wasn't. Oops.

• https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for-github-actions#onpushpull_requestpull_request_targetpathspaths-ignore
• https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for-github-actions#filter-pattern-cheat-sheet