GitHub workflows should use more restrictive bazel cache line

[proppy]

Currently we use {{ github.sha1 }} as the main cache line for storing bazel cache in GitHub actions.

This effectively cause a new cache to be created on each commit eating precious cache quota and potentially slowing down the cache action post run step (as it need to upload a brand new cache).

https://github.com/actions/cache/blob/main/examples.md#---bazel suggests to use:

    key: ${{ runner.os }}-bazel-${{ hashFiles('.bazelversion', '.bazelrc', 'WORKSPACE', 'WORKSPACE.bazel', 'MODULE.bazel') }}

We could use a derivative of this, that also include dependency_support bzl files to only re-upload a new cache when the project dependencies change.

This would have the side effect of not refreshing the cache of the main XLS build anymore, but that's not where we spend the most of our build time anyway.

[cdleary]

@hongted may have thoughts on this -- it took a little work for us to get the caching to a point where it wouldn't overflow.