Downgrade severity of field naming violation

Existing fields are being marked as Errors because they violate the
naming standards established in .editorconfig. But since the names
already exist, and changing some would be a breaking change, better to
relax the setting to "suggestion" instead of "error".

.editorconfig

@@ -182,7 +182,7 @@ dotnet_naming_rule.types_should_be_pascal_case.severity = error
 dotnet_naming_rule.types_should_be_pascal_case.symbols = types
 dotnet_naming_rule.types_should_be_pascal_case.style = pascal_case
 
-dotnet_naming_rule.non_field_members_should_be_pascal_case.severity = error
+dotnet_naming_rule.non_field_members_should_be_pascal_case.severity = suggestion
 dotnet_naming_rule.non_field_members_should_be_pascal_case.symbols = non_field_members
 dotnet_naming_rule.non_field_members_should_be_pascal_case.style = pascal_case