Cache submodule metadata alongside external sources

.gitea/workflows/build.yml

@@ -60,8 +60,8 @@ jobs:
           EXTERNAL_ARCHIVE="${CACHE_ROOT}/external-${EXTERNAL_CACHE_KEY}.tar.zst"
           if [ -f "${EXTERNAL_ARCHIVE}" ]; then
             echo "Restoring external cache from ${EXTERNAL_ARCHIVE}"
-            rm -rf external
-            mkdir -p external
+            rm -rf external .git/modules/external
+            mkdir -p external .git/modules
             tar --zstd -xf "${EXTERNAL_ARCHIVE}"
             echo "EXTERNAL_CACHE_HIT=true" >> "$GITHUB_ENV"
           else
@@ -70,10 +70,9 @@ jobs:
           fi
 
       - name: Sync submodules
-        if: env.EXTERNAL_CACHE_HIT != 'true'
         run: |
           git submodule sync --recursive
-          git submodule update --init --recursive --depth 1
+          git submodule update --init --recursive --depth 1 --jobs "$(nproc)"
 
       - name: Install dependencies
         run: |
@@ -124,7 +123,7 @@ jobs:
           EXTERNAL_ARCHIVE="${CACHE_ROOT}/external-${EXTERNAL_CACHE_KEY}.tar.zst"
           mkdir -p "${CACHE_ROOT}"
           if [ ! -f "${EXTERNAL_ARCHIVE}" ]; then
-            tar --zstd -cf "${EXTERNAL_ARCHIVE}" external
+            tar --zstd -cf "${EXTERNAL_ARCHIVE}" external .git/modules/external
           fi
 
       - name: Save depends cache