ci: cache clang tidy even if it fails

One failure will otherwise cause us to lose the entire cache

.github/workflows/CI.yaml

@@ -219,8 +219,8 @@ jobs:
         git checkout bd1620a8609ddaf2f64500820abc8b4d150edeaf # v1.1.0
         ./install-user-client
 
-    - name: Cache Clang Tidy
-      uses: actions/cache@v3.3.2
+    - name: Restore Clang Tidy cache
+      uses: actions/cache/restore@v3.3.2
       with:
         # since the ctcache is just a list of checksums that were checked, we want to write to it every ci run to keep it up to date
         # otherwise github actions just restores some old cache if the key didn't change
@@ -242,6 +242,15 @@ jobs:
         cd build
         PATH=~/.local/bin:"$PATH" CTCACHE_DIR=/tmp/ci-ctcache ../util/clang-tidy.sh
 
+  - name: Save Clang Tidy cache
+    uses: actions/cache/save@v3.3.2
+    # always run, except if the workflow was cancelled
+    # this means clang tidy will get cached even if some checks are failing
+    if: success() || failure()
+    with:
+      path: /tmp/ci-ctcache
+      key: clang-tidy-ctcache-${{ github.run_id }}
+
   appstream-news-validate:
     name: AppStream and News validate
     runs-on: ubuntu-22.04