Run clang-format only over files changed in the PR

.github/check-c-formatting.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env sh
+# I wanted to get the merge base using {{ github.base_ref }}, however this is only
+# available for the event that opens the PR or edits it, not on pushes to the branch.
+# Comparing to main should be an OK alternative, since it will - at worst - do more
+# autoformatting than it otherwise would.
+
+[ -z "$1" ] && merge_base=main || merge_base="$1"
+
+git fetch origin $merge_base:refs/remotes/origin/$merge_base
+
+(git diff --name-only "origin/$merge_base") | while read filename; do
+    extension="${filename##*.}"
+    if [ "$extension" = "c" ] || [ "$extension" = "h" ]; then
+        clang-format -i -style=file "$filename"
+    fi
+done

.github/workflows/linting.yml

@@ -9,9 +9,7 @@ jobs:
       - name: Check out openvas-scanner
         uses: actions/checkout@v4
       - name: Formatting
-        run: |
-          clang-format -i -style=file {src,misc,nasl}/*.{c,h}
-          git diff --exit-code
+        run: sh .github/check-c-formatting.sh ${{ github.base_ref }}
   Rust:
     runs-on: ubuntu-latest
     defaults: