fix(ci): use fixed path for ccache dir to survive workspace changes

The Gitea runner assigns a different workspace directory hash on each
run (e.g. /var/lib/gitea-runner/.cache/act/<hash>/hostexecutor/). When
CCACHE_DIR was set to ${{ github.workspace }}/.ccache, the actions/cache
save and restore operated on a path that changed every run, making the
restored cache land in the wrong location. This caused 0% hit rate on
the second build despite the cache being saved successfully.

Fix by using a fixed path (/tmp/ccache-kindred-create) for CCACHE_DIR
and the cache action path. CCACHE_BASEDIR remains set to the workspace
so ccache stores relative source paths, making cache entries portable
across different workspace directories.

.gitea/workflows/build.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: app-builder
 
     env:
-      CCACHE_DIR: ${{ github.workspace }}/.ccache
+      CCACHE_DIR: /tmp/ccache-kindred-create
       CCACHE_COMPRESS: "true"
       CCACHE_COMPRESSLEVEL: "6"
       CCACHE_MAXSIZE: "4G"
@@ -69,7 +69,7 @@ jobs:
         id: ccache-restore
         uses: https://github.com/actions/cache/restore@v4
         with:
-          path: ${{ github.workspace }}/.ccache
+          path: /tmp/ccache-kindred-create
           key: ccache-build-${{ github.ref_name }}-${{ github.sha }}
           restore-keys: |
             ccache-build-${{ github.ref_name }}-
@@ -107,7 +107,7 @@ jobs:
         if: always()
         uses: https://github.com/actions/cache/save@v4
         with:
-          path: ${{ github.workspace }}/.ccache
+          path: /tmp/ccache-kindred-create
           key: ccache-build-${{ github.ref_name }}-${{ github.sha }}
 
       - name: Run C++ unit tests

.gitea/workflows/release.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: app-builder
 
     env:
-      CCACHE_DIR: ${{ github.workspace }}/.ccache
+      CCACHE_DIR: /tmp/ccache-kindred-create
       CCACHE_COMPRESS: "true"
       CCACHE_COMPRESSLEVEL: "6"
       CCACHE_MAXSIZE: "4G"
@@ -77,7 +77,7 @@ jobs:
         id: ccache-restore
         uses: https://github.com/actions/cache/restore@v4
         with:
-          path: ${{ github.workspace }}/.ccache
+          path: /tmp/ccache-kindred-create
           key: ccache-release-${{ github.ref_name }}-${{ github.sha }}
           restore-keys: |
             ccache-release-
@@ -116,7 +116,7 @@ jobs:
         if: always()
         uses: https://github.com/actions/cache/save@v4
         with:
-          path: ${{ github.workspace }}/.ccache
+          path: /tmp/ccache-kindred-create
           key: ccache-release-${{ github.ref_name }}-${{ github.sha }}
 
       - name: Build .deb package