ci(pr_test_build_images): Fix krb5 version in versions.toml

Author: NickLarsenNZ

krb5/versions.toml

@@ -1,4 +1,4 @@
-[versions."0.21.1"]
+[versions."1.21.1"]
 build_on_pr = true
 # This will come later. See: https://github.com/stackabletech/docker-images/issues/770
 # dependencies = { ... }