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/actions/pgsql-shard/action.yml

@@ -34,7 +34,7 @@ runs:
       env:
         # pgsql is chosen to be the unlucky one to run with the slow "race detector", it is about 60% slower.
         GOTEST_FLAGS: -race -timeout=40m
-        TAGS: bindata gogit
+        TAGS: bindata
         TEST_LDAP: 1
         TEST_SHARD: ${{ inputs.shard }}
         TEST_TOTAL_SHARDS: ${{ inputs.total-shards }}