Bump github.com/mattermost/mattermost-server/v6 from 6.1.0 to 6.3.0 (#1686)

Bumps [github.com/mattermost/mattermost-server/v6](https://github.com/mattermost/mattermost-server) from 6.1.0 to 6.3.0.
- [Release notes](https://github.com/mattermost/mattermost-server/releases)
- [Changelog](https://github.com/mattermost/mattermost-server/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mattermost/mattermost-server/compare/v6.1.0...v6.3.0)

---
updated-dependencies:
- dependency-name: github.com/mattermost/mattermost-server/v6
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

vendor/golang.org/x/crypto/ssh/keys.go

@@ -939,6 +939,15 @@ func newDSAPrivateKey(key *dsa.PrivateKey) (Signer, error) {
 	return &dsaPrivateKey{key}, nil
 }
 
+type rsaSigner struct {
+	AlgorithmSigner
+	defaultAlgorithm string
+}
+
+func (s *rsaSigner) Sign(rand io.Reader, data []byte) (*Signature, error) {
+	return s.AlgorithmSigner.SignWithAlgorithm(rand, data, s.defaultAlgorithm)
+}
+
 type wrappedSigner struct {
 	signer crypto.Signer
 	pubKey PublicKey