Process Spawner: protect against races between TERM and KILL

Because a task (usually a test) can simply finish by itself, either
before a TERM or between a TERM and a KILL, it's important to protect
against the process not existing anymore.

   File "/Users/runner/work/avocado/avocado/avocado/plugins/spawners/process.py",
   line 87, in terminate_task
   runtime_task.spawner_handle.process.kill()
   File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/asyncio/subprocess.py",
   line 143, in kill
   self._transport.kill()
   File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/asyncio/base_subprocess.py",
   line 153, in kill
   self._check_proc()
   File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/asyncio/base_subprocess.py",
   line 142, in _check_proc
   raise ProcessLookupError()

The following is an exercept from a stacktrace when the situation
hits.

Signed-off-by: Cleber Rosa <[email protected]>

avocado/plugins/spawners/process.py

@@ -74,7 +74,10 @@ async def wait_task(runtime_task):  # pylint: disable=W0221
         await runtime_task.spawner_handle.wait_task
 
     async def terminate_task(self, runtime_task):
-        runtime_task.spawner_handle.process.terminate()
+        try:
+            runtime_task.spawner_handle.process.terminate()
+        except ProcessLookupError:
+            return True
         soft_interval = self.config.get(
             "runner.task.interval.from_soft_to_hard_termination"
         )
@@ -84,7 +87,10 @@ async def terminate_task(self, runtime_task):
                 runtime_task.spawner_handle.process.wait(), soft_interval
             )
         except asyncio.TimeoutError:
-            runtime_task.spawner_handle.process.kill()
+            try:
+                runtime_task.spawner_handle.process.kill()
+            except ProcessLookupError:
+                return True
             hard_interval = self.config.get(
                 "runner.task.interval.from_hard_termination_to_verification"
             )