Disable running slow CI for doc-only changes

[ghpvnist]

While getting #9065 reviewed, I noticed that we're running expensive (and long) CI even for no-op changes like removing trailing whitespaces from markdown files.

Note that this only skips CI when the entire PR only consists of markdown changes. Removing the CI for comments are more difficult. However, this is a step in the right direction to save some resources and enable merging PRs faster.

fixes #9073

[tengyifei]

Currently we require that the CPU and TPU tests must pass before a PR can be landed.

If these checks are skipped, will that prevent any markdown changes from landing, since GitHub checks would look like this:

[ghpvnist]

Okay I've done some testing on my fork. It should trigger the workflows when there are code changes. If PR only has markdown changes, it should return success early and skip running the actual tests.

[tengyifei]

Thanks! The logic looks sensible to me, but looks like the workflow file has a syntax error:

[tengyifei]

@ghpvnist still not works:

Invalid workflow file: .github/workflows/build_and_test.yml#L54
The workflow is not valid. .github/workflows/build_and_test.yml (Line: 54, Col: 9): Unexpected value 'secrets' .github/workflows/build_and_test.yml (Line: 44, Col: 5): Required property is missing: runs-on