test: Sort tested dimensions dict by keys on A/B test failures

When A/B test fails, it prints the tested dimensions, but it was not
sorted and was not easy for human to read.

Signed-off-by: Takahiro Itazuri <[email protected]>

tools/ab_test.py

@@ -315,7 +315,7 @@ def ab_performance_test(
                 f"for metric \033[1m{metric}\033[0m with \033[0;31m\033[1mp={result.pvalue}\033[0m. "
                 f"This means that observing a change of this magnitude or worse, assuming that performance "
                 f"characteristics did not change across the tested commits, has a probability of {result.pvalue:.2%}. "
-                f"Tested Dimensions:\n{json.dumps(dict(dimension_set), indent=2)}"
+                f"Tested Dimensions:\n{json.dumps(dict(dimension_set), indent=2, sort_keys=True)}"
             )
             messages.append(msg)