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/github.com/minio/minio-go/v7/post-policy.go

@@ -316,8 +316,8 @@ func (p PostPolicy) marshalJSON() []byte {
 	}
 	retStr := "{"
 	retStr = retStr + expirationStr + ","
-	retStr = retStr + conditionsStr
-	retStr = retStr + "}"
+	retStr += conditionsStr
+	retStr += "}"
 	return []byte(retStr)
 }