chore: improve preparing tests

- Only prepare repositories once.
- Move the repositories to temporary directories (these should usually be stored in
memory) which are recreated for each test to avoid persistentance
between tests. Doing some dirty profiling suggests that the preparing
test functions from 140-100ms to 70-40ms

tests/integration/git_clone_wiki_test.go

@@ -13,7 +13,6 @@ import (
 
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/util"
-	"code.gitea.io/gitea/tests"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -33,8 +32,6 @@ func assertFileEqual(t *testing.T, p string, content []byte) {
 
 func TestRepoCloneWiki(t *testing.T) {
 	onGiteaRun(t, func(t *testing.T, u *url.URL) {
-		defer tests.PrepareTestEnv(t)()
-
 		dstPath := t.TempDir()
 
 		r := fmt.Sprintf("%suser2/repo1.wiki.git", u.String())