Reword security contact description for clarity

This doesn't change the contact, just rewords it to avoid possible
future ambiguity, now that the repository is in an org. See #1632.

Author: EliahKagan

SECURITY.md

@@ -5,6 +5,6 @@
 Please feel free to [draft a GitHub advisory](https://github.com/GitoxideLabs/gitoxide/security/advisories/new), and I will work with you to disclose and or resolve the issue
 responsibly.
 
-If this doesn't seem like the right approach or there are questions, please feel free to reach out to the @icloud.com email used in my commits.
+If this doesn't seem like the right approach or there are questions, please feel free to reach out to the email used in Sebastian Thiel's commits.
 
 Thank you.