pin used actions

plus some reordering and harmonization across files

.github/workflows/desktop-lint.yml

@@ -1,7 +1,7 @@
 name: Code Style (C++) 
 
 permissions:
-  contents: read
+  contents: read    # needed to checkout repo
 
 on:
   # Push trigger not needed for linting, we do not allow direct pushes to master
@@ -21,11 +21,12 @@ on:
 
 jobs:
   format:
-    runs-on: ubuntu-slim
+    name: "Check formatting"
+    runs-on: ubuntu-slim    # https://github.com/actions/runner-images/blob/main/images/ubuntu-slim/ubuntu-slim-Readme.md
 
     steps:
     - name: "Checkout"
-      uses: actions/checkout@v7
+      uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
       with:
         fetch-depth: 20    # should be enough to find merge base