CI: Add concurrency groups and permissions limitations

Author: effigies

.github/workflows/pre-release.yml

@@ -18,6 +18,13 @@ defaults:
   run:
     shell: bash
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
 jobs:
   pre-release:
     # Check pre-releases of dependencies on stable Python

.github/workflows/stable.yml

@@ -24,6 +24,13 @@ defaults:
   run:
     shell: bash
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
 jobs:
   build:
     runs-on: ubuntu-latest