Add SendGrid to list of public repo secret scanning partners (#18830)

Author: Grey Baker

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

@@ -53,6 +53,7 @@ PyPI | PyPI API Token
 RubyGems | RubyGems API Key
 Samsara | Samsara API Token
 Samsara | Samsara OAuth Access Token
+SendGrid | SendGrid API Key
 Shopify | Shopify App Shared Secret
 Shopify | Shopify Access Token
 Shopify | Shopify Custom App Access Token