refactor!: remove go-git backend (#39487)

Removes the go-git backend so every build uses the git CLI backend. Its
Windows performance advantage is gone, it lacks SHA-256 support, and it
breaks repositories on Windows.

The performance changes moved to
https://github.com/go-gitea/gitea/pull/39526.

Fixes https://github.com/go-gitea/gitea/issues/38359
Fixes https://github.com/go-gitea/gitea/issues/34694

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

.github/workflows/cache-seeder.yml

@@ -37,22 +37,15 @@ jobs:
       - uses: ./.github/actions/go-setup
       - run: make deps-backend deps-tools
       - run: TAGS="bindata" make backend
-      - run: TAGS="bindata gogit" make backend
       - name: warm test compile cache (bindata)
         env:
           TAGS: bindata
           GOTEST_FLAGS: -race -list=^$$ -count=1
         run: make test-backend
-      - name: warm test compile cache (bindata gogit)
-        env:
-          TAGS: bindata gogit
-          GOTEST_FLAGS: -race -list=^$$ -count=1
-        run: make test-backend
       - name: warm integration compile cache
         run: |
           TAGS="bindata" make test-integration-compile
-          TAGS="bindata gogit" make test-integration-compile
-          TAGS="bindata gogit" GOTEST_FLAGS="-race" make test-integration-compile
+          TAGS="bindata" GOTEST_FLAGS="-race" make test-integration-compile
 
   lint:
     runs-on: ubuntu-latest