Allow customizing the `GITHUB_SERVER_URL` for GHE instances

Describe the enhancement

Currently, we have the Github URL hardcoded to :

  const treeUrl = `https://api.github.com/repos/${owner}/${repo}/git/trees/${branch}`

https://github.com/actions/toolkit/blob/main/packages/tool-cache/src/tool-cache.ts#L596C9-L596C16

While that's fine for github.com users, that tends to cause rate limiting issues for GHE users such as

API rate limit exceeded for xxx. (But here's the good news: Authenticated requests get a higher rate limit. Check out the documentation for more details.)

This is seen in action for setup-go for example as a call such as :

const releases = await tc.getManifestFromRepo(
  'actions',
  'go-versions',
  auth,
  'main'
);

Builds a call to https://api.github.com/repos/actions/go-versions/git/trees/main triggering the rate limits error explained above

Additional information

Can we leverage process.env['GITHUB_SERVER_URL' ?

Example :

https://github.com/actions/checkout/blob/72f2cec99f417b1a1c5e2e88945068983b7965f9/src/url-helper.ts#L22-L45

Note to maintainers

If accepted, It'd be happy to pick this up

Start in packages/tool-cache/src/tool-cache.ts at the hardcoded treeUrl construction, then compare the URL handling in actions/checkout's src/url-helper.ts. Trace getManifestFromRepo to confirm the generated request uses the configured GitHub Enterprise server URL instead of api.github.com. Done means GHE users can retrieve manifests without the github.com rate-limit failure.