fix(insomnia-test): use import.meta.dirname instead of __dirname in ESM specs

insomnia-test is "type": "module", so __dirname is undefined and
`playwright test --list` collected 0 tests, failing the Shard Matrix job.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

packages/insomnia-test/tests/grpc-request/mtls-client-certificate.spec.ts

@@ -17,7 +17,7 @@ test("Verify Client Certificate Toggle Controls mTLS Enforcement For gRPC Reques
 
   await preferencesFlow.set({
     validateSSL: false,
-    dataFolders: [path.join(__dirname, "../../misc/fixtures")],
+    dataFolders: [path.join(import.meta.dirname, "../../misc/fixtures")],
   });
 
   const project = await workspaceFlow.createProject(