ci/update_traces_checksum.py: check if checksum is in the array, not it's value

Fixes: 45eda06953 ("ci: introduce update_traces_checksum.py")

Reviewed-by: Guilherme Gallo <guilherme.gallo@collabora.com>
Signed-off-by: David Heidelberg <david.heidelberg@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19510>

.gitlab-ci/bin/update_traces_checksum.py

@@ -90,10 +90,7 @@ def gather_results(
                         print(f"Trace {trace} crashed")
                         continue
 
-                    if (
-                        checksum in target['traces'][trace][dev_name] and
-                        target['traces'][trace][dev_name]['checksum'] == checksum
-                    ):
+                    if target['traces'][trace][dev_name].get('checksum') == checksum:
                         continue
 
                     if "label" in target['traces'][trace][dev_name]: