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
...

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

vendor/github.com/vmihailenco/msgpack/v5/safe.go

@@ -0,0 +1,13 @@
+// +build appengine
+
+package msgpack
+
+// bytesToString converts byte slice to string.
+func bytesToString(b []byte) string {
+	return string(b)
+}
+
+// stringToBytes converts string to byte slice.
+func stringToBytes(s string) []byte {
+	return []byte(s)
+}