t/lib-credential: clean additional credential

71201ab0e5 (t/lib-credential.sh: ensure credential helpers handle long
headers, 2023-05-01) added a test which stores credentials with the host
victim.example.com but this was never cleaned up, leaving residual data
in the credential store after running the tests.

Add a cleanup call for this credential to resolve this issue.

Signed-off-by: Bo Anderson <mail@boanderson.me>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-credential.sh

@@ -50,6 +50,7 @@ helper_test_clean() {
 	reject $1 https example.com user-overwrite
 	reject $1 https example.com user-erase1
 	reject $1 https example.com user-erase2
+	reject $1 https victim.example.com user
 	reject $1 http path.tld user
 	reject $1 https timeout.tld user
 	reject $1 https sso.tld