gl-client-py: make retry_for optional

retry_for argument in pay is optional in core-lightning
let's keep it that way also during tests.

We were trying to intercept pay requests and redirect them to xpay and
renepay but with retry_for=0 renepay would inmediately fail.

Signed-off-by: Lagrang3 <[email protected]>

Author: Lagrang3

libs/gl-client-py/glclient/__init__.py

@@ -397,7 +397,7 @@ def pay(
         self,
         bolt11: str,
         amount_msat: Optional[clnpb.Amount] = None,
-        retry_for: int = 0,
+        retry_for: Optional[int] = None,
         maxfee: Optional[clnpb.Amount] = None,
         maxfeepercent: Optional[float] = None,
     ) -> clnpb.PayResponse: