defer cancel() leaks memory (#748)

* defer cancel() leaks memory

* Update interceptors/retry/retry.go

Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

---------

Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

Author: JacobSMoller

interceptors/retry/retry.go

@@ -44,8 +44,10 @@ func UnaryClientInterceptor(optFuncs ...CallOption) grpc.UnaryClientInterceptor
 				callOpts.onRetryCallback(parentCtx, attempt, lastErr)
 			}
 			callCtx, cancel := perCallContext(parentCtx, callOpts, attempt)
-			defer cancel() // Clean up potential resources.
 			lastErr = invoker(callCtx, method, req, reply, cc, grpcOpts...)
+			// Cancel the context immediately after invoking the next call in the chain to avoid
+			// holing onto its memory until this function returns.
+			cancel()
 			// TODO(mwitkow): Maybe dial and transport errors should be retriable?
 			if lastErr == nil {
 				return nil