doc: add mention to GPG_TTY

PR-URL: #51806
Reviewed-By: Beth Griggs <bethanyngriggs@gmail.com>
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>
Reviewed-By: Ruy Adorno <ruyadorno@google.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/contributing/releases.md

@@ -883,6 +883,12 @@ same GPG key!**
 Use `tools/release.sh` to promote and sign the build. Before doing this, you'll
 need to ensure you've loaded the correct ssh key, or you'll see the following:
 
+If your GPG key is protected by a password, you might need to run:
+
+```console
+$ export GPG_TTY=$(tty)
+```
+
 ```console
 # Checking for releases ...
 Enter passphrase for key '/Users/<user>/.ssh/id_rsa':