test(cli): isolate config tests from CI environment variables

Unset CI and GITHUB_ACTIONS environment variables in config.test.ts to
   ensure tests that rely on interactive/TTY mode pass correctly in CI
   environments.

   The isHeadlessMode detection logic defaults to non-interactive mode if
   these variables are present, which previously caused assertion failures
   in tests expecting interactive startup messages and specific tool
   exclusion behaviors.

packages/cli/src/config/config.test.ts

@@ -162,11 +162,15 @@ vi.mock('./extension-manager.js', () => {
 // Global setup to ensure clean environment for all tests in this file
 const originalArgv = process.argv;
 const originalGeminiModel = process.env['GEMINI_MODEL'];
+const originalCI = process.env['CI'];
+const originalGithubActions = process.env['GITHUB_ACTIONS'];
 const originalStdoutIsTTY = process.stdout.isTTY;
 const originalStdinIsTTY = process.stdin.isTTY;
 
 beforeEach(() => {
   delete process.env['GEMINI_MODEL'];
+  delete process.env['CI'];
+  delete process.env['GITHUB_ACTIONS'];
   // Restore ExtensionManager mocks by re-assigning them
   ExtensionManager.prototype.getExtensions = vi.fn().mockReturnValue([]);
   ExtensionManager.prototype.loadExtensions = vi
@@ -193,6 +197,16 @@ afterEach(() => {
   } else {
     delete process.env['GEMINI_MODEL'];
   }
+  if (originalCI !== undefined) {
+    process.env['CI'] = originalCI;
+  } else {
+    delete process.env['CI'];
+  }
+  if (originalGithubActions !== undefined) {
+    process.env['GITHUB_ACTIONS'] = originalGithubActions;
+  } else {
+    delete process.env['GITHUB_ACTIONS'];
+  }
   Object.defineProperty(process.stdout, 'isTTY', {
     value: originalStdoutIsTTY,
     configurable: true,