Fix perf scenarios in the min_opt config (dotnet#20010)

The appropriate environment variables were not being set due to a name mismatch

Author: kouvel

tests/scripts/run-xunit-perf.py

@@ -455,7 +455,7 @@ def main(args):
     build_perfharness(coreclrRepo, sandboxDir, extension, myEnv)
 
     # Set up environment for running tests
-    if optLevel == 'min_opts':
+    if optLevel == 'min_opt':
         myEnv['COMPlus_JITMinOpts'] = '1'
         myEnv['COMPlus_TieredCompilation'] = '0'
     elif optLevel == 'full_opt':