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/pull-compliance.yml

@@ -93,13 +93,13 @@ jobs:
         env:
           GOOS: linux
           GOARCH: arm64
-          TAGS: bindata gogit
+          TAGS: bindata
       - name: build-backend-windows
         run: go build -ldflags '-s -w' -o gitea-windows
         env:
           GOOS: windows
           GOARCH: amd64
-          TAGS: bindata gogit
+          TAGS: bindata
       - name: build-backend-386
         run: go build -ldflags '-s -w' -o gitea-linux-386
         env: