[CI][Github] Add Workflow to Run Python Tests in CI Folder (#148696)

This patch adds a new GHA workflow that runs pytest inside of the .ci
directory to test all of the CI infrastructure. This is to make it more
visible to new contributors that these tests exist and also to ensure
that they are passing before merge. There have been several instances
already where someone neglected to update these tests and we should have
automation to enforce this.

.github/workflows/check-ci.yml

@@ -0,0 +1,37 @@
+name: Check CI Scripts
+
+permissions:
+  contents: read
+
+on:
+  push:
+    paths:
+     - '.ci/**'
+     - '.github/workflows/check-ci.yml'
+  pull_request:
+    paths:
+     - '.ci/**'
+     - '.github/workflows/check-ci.yml'
+
+jobs:
+  test-python:
+    name: "Check Python Tests"
+    runs-on: ubuntu-24.04
+    if: github.repository == 'llvm/llvm-project'
+    steps:
+      - name: Fetch LLVM sources
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          sparse-checkout: .ci
+      - name: Setup Python
+        uses: actions/setup-python@42375524e23c412d93fb67b49958b491fce71c38 # v5.4.0
+        with:
+          python-version: 3.13
+          cache: 'pip'
+      - name: Install Python Dependencies
+        run: |
+          pip3 install -r .ci/all_requirements.txt
+          pip3 install pytest==8.4.1
+      - name: Run Tests
+        working-directory: .ci
+        run: pytest