Don't set Cache-Control headers for git archives

Rails already sets Cache-Control according to the project visibility.
Always setting the header value to `private` prevents us from doing
proper caching (e.g. at CDN level) for public projects.

Related to https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/6829

internal/git/archive.go

@@ -166,7 +166,6 @@ func setArchiveHeaders(w http.ResponseWriter, format gitalypb.GetArchiveRequest_
 		w.Header().Set("Content-Type", "application/octet-stream")
 	}
 	w.Header().Set("Content-Transfer-Encoding", "binary")
-	w.Header().Set("Cache-Control", "private")
 }
 
 func prepareArchiveTempfile(dir string, prefix string) (*os.File, error) {

internal/git/archive_test.go

@@ -67,13 +67,15 @@ func TestSetArchiveHeaders(t *testing.T) {
 		w.Header().Set("Content-Type", "test")
 		w.Header().Set("Content-Length", "test")
 		w.Header().Set("Content-Disposition", "test")
-		w.Header().Set("Cache-Control", "test")
+
+		// This should be preserved
+		w.Header().Set("Cache-Control", "public, max-age=3600")
 
 		setArchiveHeaders(w, testCase.in, "filename")
 
 		testhelper.AssertResponseWriterHeader(t, w, "Content-Type", testCase.out)
 		testhelper.AssertResponseWriterHeader(t, w, "Content-Length")
 		testhelper.AssertResponseWriterHeader(t, w, "Content-Disposition", `attachment; filename="filename"`)
-		testhelper.AssertResponseWriterHeader(t, w, "Cache-Control", "private")
+		testhelper.AssertResponseWriterHeader(t, w, "Cache-Control", "public, max-age=3600")
 	}
 }