Bump GoSAML dependency (#20092)

```release-note
NONE
```

go.mod

@@ -38,7 +38,7 @@ require (
 	github.com/ledongthuc/pdf v0.0.0-20220302134840-0c2507a12d80
 	github.com/lib/pq v1.10.4
 	github.com/mattermost/go-i18n v1.11.1-0.20211013152124-5c415071e404
-	github.com/mattermost/gosaml2 v0.8.0
+	github.com/mattermost/gosaml2 v0.8.1-0.20220428161029-8c99721fdec4
 	github.com/mattermost/gziphandler v0.0.1
 	github.com/mattermost/ldap v0.0.0-20201202150706-ee0e6284187d
 	github.com/mattermost/logr/v2 v2.0.15