fix: correctly shutdown xcom after job is complete

I got the following logs when using the original statement

```
docker run -u 1000 -it alpine sh # alpine container seems to be run under uid 1000 in kubernetes
sh -c trap "exit 0" INT; while true; do sleep 1; done;
````

```
kill -2 $(pgrep -u $(whoami) -f 'trap')
```

```
whoami
whoami: unknown uid 1000
```

```
pgrep -f 'trap' # returns no processes
```

instead with:

```
kill -2 $(pgrep -u $(id -u) -f 'sh')
```

Signed-off-by: Kasper J. Hermansen <[email protected]>

providers/src/airflow/providers/cncf/kubernetes/utils/pod_manager.py

@@ -855,7 +855,7 @@ def extract_xcom_kill(self, pod: V1Pod):
                 _preload_content=False,
             )
         ) as resp:
-            self._exec_pod_command(resp, "kill -2 $(pgrep -u $(whoami) -f trap)")
+            self._exec_pod_command(resp, "kill -2 $(pgrep -u $(id -u) -f 'sh')")
 
     def _exec_pod_command(self, resp, command: str) -> str | None:
         res = ""