boot-qemu.py: Workaround PLW1509 warning from Ruff

This is the same warning from pylint that was disabled in
ClangBuiltLinux/actions-workflows#5.

  boot-qemu.py:216:35: PLW1509 `preexec_fn` argument is unsafe when using threads

'preexec_fn' is on the path towards deprecation, so workaround this
warning by refactoring the code to use the new keyword argument
'process_group' when using Python 3.11 and newer, which makes it clear
that we don't need 'preexec_fn' longterm. This conveniently hides the
'preexec_fn' use in Popen() so there is no more warning.

Link: https://beta.ruff.rs/docs/rules/subprocess-popen-preexec-fn/
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Author: nathanchance

boot-qemu.py

@@ -212,8 +212,17 @@ def _run_gdb(self):
                 utils.die('Port 1234 is already in use, is QEMU running?')
 
             utils.green('Starting QEMU with gdb connection on port 1234...')
-            with subprocess.Popen(qemu_cmd,
-                                  preexec_fn=os.setpgrp) as qemu_proc:
+            # setpgrp() is equivalent to setpgid(0, 0). The 'process_group'
+            # keyword argument is equivalent to calling setpgid(0, arg) but it
+            # is only available in Python 3.11 and newer.
+            if sys.version_info >= (3, 11, 0):
+                popen_kwargs = {'process_group': 0}
+            else:
+                popen_kwargs = {'preexec_fn': os.setpgrp}
+            # pylint seems to think process_group will be used with Python 3.10
+            # and earlier?
+            # pylint: disable-next=unexpected-keyword-arg
+            with subprocess.Popen(qemu_cmd, **popen_kwargs) as qemu_proc:
                 utils.green(f"Starting {self.gdb_bin}...")
                 with subprocess.Popen(gdb_cmd) as gdb_proc, \
                      contextlib.suppress(KeyboardInterrupt):