Added mypy github CI

Author: Lukas Molleman

.github/workflows/runtests.yml

@@ -30,3 +30,20 @@ jobs:
 
       - name: Run Ruff on the sympy benchmark package
         run: ruff check .
+
+  # ----------------------------- mypy ----------------------------- #
+
+  mypy:
+    needs: code-quality
+
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-python@v4
+        with:
+          python-version: '3.11'
+      - run: python -m pip install --upgrade pip
+      - run: pip install mpmath mypy
+
+      - name: Run mypy on the sympy package
+        run: mypy benchmarks slow_benchmarks