t/lib-gpg: call prepare_gnupghome() in GPG2 prereq

The GPG2 prereq added in 2f36339 (t/lib-gpg: introduce new prereq
GPG2, 2023-06-04) does not create the $GNUPGHOME directory.

Tests which use the GPG2 prereq without previously using the GPG prereq
fail because of the missing directory.  This currently affects
t1016-compatObjectFormat.

Ensure $GNUPGHOME is created in the GPG2 prereq.

Signed-off-by: Todd Zullinger <tmz@pobox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: tmzullinger

t/lib-gpg.sh

@@ -66,6 +66,7 @@ test_lazy_prereq GPG2 '
 		exit 1
 		;;
 	*)
+		prepare_gnupghome &&
 		(gpgconf --kill all || : ) &&
 		gpg --homedir "${GNUPGHOME}" --import \
 			"$TEST_DIRECTORY"/lib-gpg/keyring.gpg &&