Bump the # of commits searched for perf baseline

The previous value of 75 meant that a feature branch with
more than 75 commits would get spurious CI passes.

This affects #18692, but does not fix that ticket, because
if a baseline cannot be found, we should fail, not succeed.

testsuite/driver/perf_notes.py

@@ -342,7 +342,7 @@ def append_perf_stat(stats: List[PerfStat],
 #
 
 # Max number of ancestor commits to search when compiling a baseline performance metric.
-BaselineSearchDepth = 75
+BaselineSearchDepth = 1000
 
 # (isCalculated, best fit ci test_env or None)
 BestFitCiTestEnv = (False, None) # type: Tuple[bool, Optional[TestEnv]]