mail_crypt: Update link to decryption tool

Author: cmouse

docs/core/plugins/mail_crypt.md

@@ -415,7 +415,7 @@ share the key to groups or someone with no public key.
 
 ## Decrypting Files Encrypted with mail-crypt Plugin
 
-You can use [`decrypt.rb`][decrypt.rb] to decrypt encrypted files.
+You can use [`decrypt.py`][decrypt.py] to decrypt encrypted files.
 
 ## `fs-crypt`
 
@@ -468,4 +468,4 @@ doveadm \
 
 <DoveadmComponent plugin="mail-crypt" />
 
-[decrypt.rb]: https://github.com/dovecot/tools/blob/main/dcrypt-decrypt.rb
+[decrypt.py]: https://github.com/dovecot/tools/blob/main/dcrypt-decrypt.py