Use parameter expansion for WPFF flag

Author: aidangarske

.github/scripts/pam-pkcs11-test.sh

@@ -64,8 +64,8 @@ fi
 echo "[*] Configuring pam_pkcs11..."
 
 # Temporarily unset WOLFPROV_FORCE_FAIL so we can test the failure case
-ORIG_WOLFPROV_FORCE_FAIL="$WOLFPROV_FORCE_FAIL"
-unset WOLFPROV_FORCE_FAIL
+ORIG_WOLFPROV_FORCE_FAIL="${WOLFPROV_FORCE_FAIL:-}"
+unset WOLFPROV_FORCE_FAIL || true
 
 # Generate dummy CA cert if missing
 if [ ! -f /test/certs/test-ca.crt ]; then