feat: support non-standard .mod files in go-version-file

Change `parseGoVersionFile` to match any file ending in `.mod` instead
of only `go.mod` by basename. This enables using dedicated module files
like `golangci-lint.mod` or `tools.mod` with the `go-version-file` input.

Fixes #736

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

__tests__/setup-go.test.ts

@@ -1059,6 +1059,12 @@ use .
           expected_version: version,
           desc: 'from toolchain directive'
         },
+        {
+          goVersionfile: 'golangci-lint.mod',
+          fileContents: Buffer.from(buildGoMod(placeholderVersion, version)),
+          expected_version: version,
+          desc: 'from toolchain directive in non-standard .mod file'
+        },
         {
           goVersionfile: 'go.mod',
           fileContents: Buffer.from(buildGoMod(placeholderVersion, version)),
@@ -1072,6 +1078,13 @@ use .
           gotoolchain_env: 'local',
           expected_version: placeholderVersion,
           desc: 'from go directive when GOTOOLCHAIN is local'
+        },
+        {
+          goVersionfile: 'golangci-lint.mod',
+          fileContents: Buffer.from(buildGoMod(placeholderVersion, version)),
+          gotoolchain_env: 'local',
+          expected_version: placeholderVersion,
+          desc: 'from go directive in non-standard .mod file when GOTOOLCHAIN is local'
         }
       ].forEach(test => {
         it(`reads version (${version}) in ${test.goVersionfile} ${test.desc}`, async () => {

src/installer.ts

@@ -654,7 +654,7 @@ export function parseGoVersionFile(versionFilePath: string): string {
   const contents = fs.readFileSync(versionFilePath).toString();
 
   if (
-    path.basename(versionFilePath) === 'go.mod' ||
+    versionFilePath.endsWith('.mod') ||
     path.basename(versionFilePath) === 'go.work'
   ) {
     // for backwards compatibility: use version from go directive if