[PORT] Remove SHA1 for support for ssh rsa signing (#31857) (#5303)

https://github.com/go-fed/httpsig seems to be unmaintained.

Switch to github.com/42wim/httpsig which has removed deprecated crypto
and default sha256 signing for ssh rsa.

No impact for those that use ed25519 ssh certificates.

This is a breaking change for:
- gitea.com/gitea/tea (go-sdk) - I'll be sending a PR there too
- activitypub using deprecated crypto (is this actually used?)

(cherry picked from commit 01dec7577a051d9bb30e91f6cf6653dc51a37d06)

---
Conflict resolution: trivial

Co-authored-by: Wim <wim@42.be>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/5303
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>

tests/integration/api_httpsig_test.go

@@ -15,7 +15,7 @@ import (
 	"code.gitea.io/gitea/modules/test"
 	"code.gitea.io/gitea/tests"
 
-	"github.com/go-fed/httpsig"
+	"github.com/42wim/httpsig"
 	"golang.org/x/crypto/ssh"
 )