Fix: fix eslint configuration

In CI, eslint is fine.

However, if I run it locally, it tries to cover the project folder and
the server folder symlink in client (already handled in ./server).

I checked that errors in client, integration-tests and server are still
properly detected.

eslint.config.mjs

@@ -19,6 +19,7 @@ export default [
       "**/out",
       "**/poky",
       "**/.vscode-test",
+      "integration-tests/project-folder",
       "__mocks__/vscode.ts",
       "**/jest.config.js",
       "**/eslint.config.mjs",