Add RubyGems as a public repo secret scanning partner (#18622)

Author: Grey Baker

data/reusables/secret-scanning/partner-secret-list-public-repo.md

@@ -50,6 +50,7 @@ Proctorio | Proctorio Registration Key
 Proctorio | Proctorio Secret Key
 Pulumi | Pulumi Access Token
 PyPI | PyPI API Token
+RubyGems | RubyGems API Key
 Samsara | Samsara API Token
 Samsara | Samsara OAuth Access Token
 Shopify | Shopify App Shared Secret