refactor: remove unnecessary moduleNameMappers from Jest config

The explicit moduleNameMappers for @actions/core and @actions/github were
not needed. The transformIgnorePatterns configuration is sufficient to
handle ESM modules from @actions packages. Only the relative import
mapper is required for TypeScript ESM compatibility.

Co-authored-by: EndBug <26386270+EndBug@users.noreply.github.com>

Author: Copilot

jest.config.mjs

@@ -5,8 +5,6 @@ export default {
   extensionsToTreatAsEsm: ['.ts'],
   moduleNameMapper: {
     '^(\\.{1,2}/.*)\\.js$': '$1',
-    '^@actions/core$': '<rootDir>/node_modules/@actions/core/lib/core.js',
-    '^@actions/github$': '<rootDir>/node_modules/@actions/github/lib/github.js',
   },
   transform: {
     '^.+\\.tsx?$': [