ci/cd: install types-pexpect

Author: itsfarseen

.github/workflows/ci.yml

@@ -17,11 +17,11 @@ jobs:
       with:
         python-version: '3.x'
     - name: Install dependencies
-      run: pip install mypy black
+      run: pip install mypy black types-pexpect
     - name: Run black
       run: black --check shellspec.py
     - name: Run mypy
-      run: mypy shellspec.py
+      run: mypy --check-untyped-defs shellspec.py
 
   docker-tests:
     runs-on: ubuntu-latest