fix: run deltachat-rpc-server in its own process group

This ensures the server does not get SIGINT
when the bot is running in a terminal and user presses ^C
We want to send SIGTERM ourselves after clean shutdown,
e.g. stopping I/O for all accounts.

deltachat-rpc-client/src/deltachat_rpc_client/rpc.py

@@ -39,6 +39,10 @@ class Rpc:
             "deltachat-rpc-server",
             stdin=subprocess.PIPE,
             stdout=subprocess.PIPE,
+            # Prevent subprocess from capturing SIGINT.
+            # We are not using `process_group`
+            # because it is not supported before Python 3.11.
+            preexec_fn=os.setpgrp,
             **self._kwargs,
         )
         self.id = 0