Improve inline documentation for what rulesets are testing

Author: jrfnl

tests/Core/Ruleset/ExpandRulesetReferenceCaseMismatch1Test.xml

@@ -1,7 +1,9 @@
 <?xml version="1.0"?>
 <ruleset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" name="ExpandRulesetReferenceTest" xsi:noNamespaceSchemaLocation="https://raw.githubusercontent.com/PHPCSStandards/PHP_CodeSniffer/master/phpcs.xsd">
 
-    <!-- Error handling: Case mismatch, will only error on case sensitive OSes. -->
+    <!-- Error handling: Case mismatch, will only error on case sensitive OSes.
+         Correct case would be: PSR12.Functions.NullableTypeDeclaration,
+         i.e. matching the case of the standard, category and sniff class name exactly. -->
     <rule ref="psr12.functions.nullabletypedeclaration"/>
 
 </ruleset>

tests/Core/Ruleset/ExpandRulesetReferenceCaseMismatch2Test.xml

@@ -1,7 +1,9 @@
 <?xml version="1.0"?>
 <ruleset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" name="ExpandRulesetReferenceTest" xsi:noNamespaceSchemaLocation="https://raw.githubusercontent.com/PHPCSStandards/PHP_CodeSniffer/master/phpcs.xsd">
 
-    <!-- Error handling: Case mismatch, will only error on case sensitive OSes. -->
+    <!-- Error handling: Case mismatch, will only error on case sensitive OSes.
+         Correct case would be: PSR12.Functions.ReturnTypeDeclaration - note the capital T in the sniff name,
+         i.e. matching the case of the standard, category and sniff class name exactly. -->
     <rule ref="PSR12.Functions.ReturntypeDeclaration"/>
 
 </ruleset>