workflow: fix typo in "python-version" variable's name

https://github.com/fphammerle/ical2vdir/commit/6a4b14a961912eeaf108102b7747d506df61ed8a

.github/workflows/python.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        python-verison: ['3.9']
+        python-version: ['3.9']
     steps:
     - uses: actions/checkout@v3
     - uses: actions/setup-python@v3