Generic/InterfaceNameSuffix: add inline comment

This commit just adds an inline comment documenting why the sniff bails
early if there is no interface name. Doing this to follow the same
pattern used by other similar sniffs like AbstractClassName
https://github.com/PHPCSStandards/PHP_CodeSniffer/blob/8a7ee56347bb4017ffc778a42a532cbb1651a20b/src/Standards/Generic/Sniffs/NamingConventions/AbstractClassNamePrefixSniff.php#L48

src/Standards/Generic/Sniffs/NamingConventions/InterfaceNameSuffixSniff.php

@@ -40,6 +40,7 @@ public function process(File $phpcsFile, $stackPtr)
     {
         $interfaceName = $phpcsFile->getDeclarationName($stackPtr);
         if ($interfaceName === null) {
+            // Live coding or parse error. Bow out.
             return;
         }