Add missing golang-json reporter to action.yml

The golang-json reporter has been fully implemented since earlier versions
but was missing from the action.yml documentation. This made it undiscoverable
for users looking for Go test support.

Changes:
- Added golang-json to the list of supported reporters in action.yml

This aligns the action.yml with:
- The actual implementation in src/main.ts (lines 264-265)
- The README.md documentation (line 145)
- The existing parser and tests

Fixes #689

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

action.yml

@@ -29,6 +29,7 @@ inputs:
         - dotnet-nunit
         - dotnet-trx
         - flutter-json
+        - golang-json
         - java-junit
         - jest-junit
         - mocha-json