tools/koji-compose.py: test with pylint and fix found issues

Check `tools/koji-compose.py` using pylint as part of GitHub actions.
Fix all issues that were found by pylint.

.github/workflows/tests.yml

@@ -88,7 +88,7 @@ jobs:
     steps:
 
       - name: Install build and test dependencies
-        run: dnf -y install python3-pylint git-core
+        run: dnf -y install python3-pylint git-core python3-requests
 
       - name: Check out code into the Go module directory
         uses: actions/checkout@v3
@@ -97,7 +97,7 @@ jobs:
 
       - name: Analysing the code with pylint
         run: |
-          python3 -m pylint dnf-json
+          python3 -m pylint dnf-json tools/koji-compose.py
 
   lint:
     name: "⌨ Lint"