Stupid question: Whenever I've used GPG to sign an email, it includes a line saying "Hash: SHA1". Does this imply PGP-signed messages are vulnerable to this, o

Stupid question: Whenever I've used GPG to sign an email, it includes a line saying "Hash: SHA1". Does this imply PGP-signed messages are vulnerable to this, or does PGP/GPG do something different/smarter?