[CI/Build] Remove dummy CI steps (#12208)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

.github/workflows/dummy.yml

-name: dummy-checks
-
-on:
-  pull_request:
-
-jobs:
-  mypy:
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        python-version: ["3.12"]
-    steps:
-      - run: echo "This is a dummy step that always passes"
-  ruff:
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        python-version: ["3.12"]
-    steps:
-      - run: echo "This is a dummy step that always passes"