I would like to run code-scanning with a custom code-scanning bundle
that already is present on my local disk. I can currently do that by
making the following hack:

1 Install bundle in tool cache:

Use toolCache.cacheDir to install the bundle with a specially crafted ID:

tc.cacheDir(localBundlePath, 'CodeQL', "0.0.0-XXX-DUMMY-BUNDLE-ID");

2 Convince codeql to look in the tool cache:

The codeql action is then invoked with a dummy URL that will make codeql.ts lookup the bundle with the specially crafted ID:

        ...
        tools: dummy://codeql-bundle-XXX-DUMMY-BUNDLE-ID/dummy
        ...

This works, but I would like a more reliable solution. I am not sure
what the best approach is for supporting my use case, but I am happy
to look into implementing a suggestion.