Fix Stryker config

Fix Stryker configuration to properly allow for some slack.

Author: martincostello

eng/stryker-config.json

@@ -21,7 +21,7 @@
     "target-framework": "net7.0",
     "thresholds": {
       "high": 100,
-      "low": 99
+      "low": 100
     }
   }
 }

src/Polly.Core/Polly.Core.csproj

@@ -7,7 +7,7 @@
     <Nullable>enable</Nullable>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <ProjectType>Library</ProjectType>
-    <MutationScore>100</MutationScore>
+    <MutationScore>99</MutationScore>
     <LegacySupport>true</LegacySupport>
     <InjectSharedSources>true</InjectSharedSources>
   </PropertyGroup>