Use string.Contains(char) instead of string.Contains(string)

with single characters

.editorconfig

@@ -150,6 +150,9 @@ dotnet_diagnostic.IDE1006.severity = warning
 # Avoid unnecessary zero-length array allocations.
 dotnet_diagnostic.CA1825.severity = warning
 
+# Use string.Contains(char) instead of string.Contains(string) with single characters.
+dotnet_diagnostic.CA1847.severity = warning
+
 ; 4-column tab indentation
 [*.yaml]
 indent_style = tab