Cache execnet gateway rinfo during WorkerController setup

Cache execnet gateway info during WorkerController setup in
order to avoid a later deadlock error triggered when pytest-cov
calls rinfo after the main thread is already busy.

Fixes: 20e3ac7 ("Use execnet main_thread_only execmodel (#1027)")

changelog/1071.bugfix

@@ -0,0 +1 @@
+Add workaround for rinfo compatibility issue with the ``execnet`` new ``main_thread_only`` "execmodel" triggered by pytest-cov (`pytest-dev/execnet#274 <https://github.com/pytest-dev/execnet/pull/274>`__ eliminates the need for this workaround).

src/xdist/workermanage.py

@@ -312,6 +312,8 @@ def shutting_down(self) -> bool:
 
     def setup(self) -> None:
         self.log("setting up worker session")
+        # Remove this after execnet is fixed in pytest-dev/execnet#274.
+        self.gateway._rinfo()
         spec = self.gateway.spec
         args = [str(x) for x in self.config.invocation_params.args or ()]
         option_dict = {}