Fix the type for LROPoller wait timeout (#21913)

Thread.join(), as called by wait(), accepts fractional seconds,
so the type for wait() should reflect that.

sdk/core/azure-core/azure/core/polling/_poller.py

@@ -257,12 +257,12 @@ def result(self, timeout=None):
 
     @distributed_trace
     def wait(self, timeout=None):
-        # type: (Optional[int]) -> None
+        # type: (Optional[float]) -> None
         """Wait on the long running operation for a specified length
         of time. You can check if this call as ended with timeout with the
         "done()" method.
 
-        :param int timeout: Period of time to wait for the long running
+        :param float timeout: Period of time to wait for the long running
          operation to complete (in seconds).
         :raises ~azure.core.exceptions.HttpResponseError: Server problem with the query.
         """