Fix partial cloning a repo (#18373) (#18377)

* Fix partial cloning a repo (#18373)

- Backport from: #18373
- Backport isn't 1-1, because the frontport had a refactor in that area,
which v1.16 doesn't have.

* Include diff & use copy

* Add partial clone test

* patch

* Apply suggestions from code review

* globalArgs first

* avoid copy but make GlobalCMDArgs append first

* please linter

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: 6543 <6543@obermui.de>

integrations/git_test.go

@@ -69,6 +69,12 @@ func testGit(t *testing.T, u *url.URL) {
 
 		t.Run("Clone", doGitClone(dstPath, u))
 
+		dstPath2, err := os.MkdirTemp("", httpContext.Reponame)
+		assert.NoError(t, err)
+		defer util.RemoveAll(dstPath2)
+
+		t.Run("Partial Clone", doPartialGitClone(dstPath2, u))
+
 		little, big := standardCommitAndPushTest(t, dstPath)
 		littleLFS, bigLFS := lfsCommitAndPushTest(t, dstPath)
 		rawTest(t, &httpContext, little, big, littleLFS, bigLFS)