Include go vendor modules for boringssl

Required for services that do not allow network access to the outside during compilation (e.g. open build service etc.).
When compiling, at least an 'export GOFLAGS="-mod=vendor"' must be done before.

.github/workflows/build.yml

@@ -22,6 +22,10 @@ jobs:
         run: |
           git config --global user.email "[email protected]"
           git config --global user.name "Your Name"
+      - name: get vendor modules
+        run: |
+          cd vendor/boringssl
+          go mod vendor
       - name: build & install
         run: |
           mkdir build && cd build
@@ -123,6 +127,7 @@ jobs:
 
       - name: build & install
         run: |
+          export GOFLAGS="-mod=vendor"
           tar -xf android-tools-*.tar.xz
           cd android-tools-*/
           test -n "${{ matrix.env1 }}" && export ${{ matrix.env1 }}