gha: set "read" permissions as default

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

.github/workflows/build.yml

@@ -1,5 +1,14 @@
 name: build
 
+# Default to 'contents: read', which grants actions to read commits.
+#
+# If any permission is set, any permission not included in the list is
+# implicitly set to "none".
+#
+# see https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#permissions
+permissions:
+  contents: read
+
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
@@ -136,6 +145,9 @@ jobs:
 
   build:
     runs-on: ubuntu-24.04
+    permissions:
+      # required to create GitHub release
+      contents: write
     steps:
       -
         name: Checkout