Cache external submodules and depends in CI

.gitea/workflows/build.yml

@@ -43,8 +43,26 @@ jobs:
       - name: Checkout
         uses: https://github.com/actions/checkout@v4
         with:
-          fetch-depth: 0
+          fetch-depth: 1
-          submodules: recursive
+          fetch-tags: true
+          submodules: false
+
+      - name: Prepare submodule cache key
+        run: |
+          git submodule status --cached --recursive > .ci-submodules.lock
+
+      - name: Restore external cache
+        id: cache-external
+        uses: https://github.com/actions/cache@v3
+        with:
+          path: external
+          key: external-${{ hashFiles('.ci-submodules.lock') }}
+
+      - name: Sync submodules
+        if: steps.cache-external.outputs.cache-hit != 'true'
+        run: |
+          git submodule sync --recursive
+          git submodule update --init --recursive --depth 1
 
       - name: Install dependencies
         run: |
@@ -65,6 +83,17 @@ jobs:
             zip \
             ${{ matrix.toolchain.packages }}
 
+      - name: Restore depends cache
+        id: cache-depends
+        uses: https://github.com/actions/cache@v3
+        with:
+          path: |
+            contrib/depends/built
+            contrib/depends/sources
+            contrib/depends/work/build
+            contrib/depends/${{ matrix.toolchain.host }}
+          key: depends-${{ matrix.toolchain.host }}-${{ hashFiles('contrib/depends/Makefile', 'contrib/depends/funcs.mk', 'contrib/depends/hosts/*.mk', 'contrib/depends/packages/*.mk', 'contrib/depends/toolchain.cmake.in') }}
+
       - name: Prepare MinGW alternatives
         if: ${{ matrix.toolchain.host == 'x86_64-w64-mingw32' || matrix.toolchain.host == 'i686-w64-mingw32' }}
         run: |