[CI] Fix printing of test report in summary view (#173314)

ffe973a3e7 changed some of the internal
APIs to return a tuple instead of just the report. This callsite was
never updated which resulted in the tuple being printed to the summary
view when we only wanted the report.

.ci/generate_test_report_github.py

@@ -16,7 +16,7 @@ if __name__ == "__main__":
     )
     args = parser.parse_args()
 
-    report = generate_test_report_lib.generate_report_from_files(
+    report, explained = generate_test_report_lib.generate_report_from_files(
         generate_test_report_lib.compute_platform_title(),
         args.return_code,
         args.build_test_logs,