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-db-tests.yml

@@ -95,17 +95,17 @@ jobs:
       - run: make deps-backend
       - run: make backend
         env:
-          TAGS: bindata gogit
+          TAGS: bindata
       - run: GITEA_TEST_DATABASE=sqlite make test-migration
         env:
-          TAGS: bindata gogit
+          TAGS: bindata
       - name: run tests
         run: GITEA_TEST_DATABASE=sqlite make test-integration
         timeout-minutes: 50
         env:
           # sqlite driver can contain large amount of Golang code, so don't use race detector for it, otherwise, extremely slow
           GOTEST_FLAGS: -timeout=40m
-          TAGS: bindata gogit
+          TAGS: bindata
 
   test-unit:
     if: needs.files-changed.outputs.backend == 'true'
@@ -163,13 +163,6 @@ jobs:
           GOTEST_FLAGS: -race -timeout=20m
           TAGS: bindata
           GITHUB_READ_TOKEN: ${{ secrets.GITHUB_READ_TOKEN }}
-      - name: unit-tests-gogit
-        run: make test-backend
-        env:
-          GOTEST_FLAGS: -race -timeout=20m
-          TAGS: bindata gogit
-          GITHUB_READ_TOKEN: ${{ secrets.GITHUB_READ_TOKEN }}
-          GITEA_TEST_CI_SKIP_EXTERNAL: true
       - run: make test-check
 
   test-mysql: