chore: skip sha256 repo for older git versions (#11542)

- Breaks testing on git versions that don't have SHA256 support.

https://codeberg.org/forgejo-integration/forgejo/actions/runs/16172/jobs/1/attempt/1#jobstep-5-2381

```
// TestLinksLogin
	"2026/03/06 06:15:20 ...ices/context/repo.go:1007:28() [E] GetBranchCommit: length 64 has no matched object format: 473a0f4c3be8a93681a267e3b1e9a7dcda1185436fe141f7749120a303721813",
```

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11542
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>
Reviewed-by: Michael Kriese <michael.kriese@gmx.de>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

tests/integration/links_test.go

@@ -9,6 +9,7 @@ import (
 	"path"
 	"testing"
 
+	"forgejo.org/modules/git"
 	"forgejo.org/modules/setting"
 	api "forgejo.org/modules/structs"
 	"forgejo.org/modules/test"
@@ -161,6 +162,10 @@ func testLinksAsUser(userName string, t *testing.T) {
 	}
 
 	for _, repo := range apiRepos {
+		if repo.ObjectFormatName == "sha256" && !git.SupportHashSha256 {
+			continue
+		}
+
 		for _, link := range repoLinks {
 			req := NewRequest(t, "GET", fmt.Sprintf("/%s/%s%s", userName, repo.Name, link))
 			session.MakeRequest(t, req, http.StatusOK)