Add pytest to dependencies in pylint workflow

.github/workflows/pylint.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install setuptools pylint codemapper openpyxl xlrd pandas ezodf
+          pip install setuptools pylint codemapper openpyxl xlrd pandas ezodf pytest
       - name: Analyzing the code with pylint
         run: |
           pylint $(git ls-files '*.py')