CI: Add concurrency and permissions to GitHub actions

Author: effigies

.github/workflows/pythonpackage.yml

@@ -10,6 +10,13 @@ on:
   pull_request:
     branches: [ master ]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
 jobs:
   build:
     runs-on: ubuntu-latest