Add clarifying comment for PS0 in commonlyQuoted list

Agent-Logs-Url: https://github.com/dotysan/shellcheck/sessions/90f001fb-db77-4304-9af4-a819f4d48f85

Co-authored-by: dotysan <5060170+dotysan@users.noreply.github.com>

Author: Copilot

src/ShellCheck/Analytics.hs

@@ -1147,7 +1147,7 @@ checkSingleQuotedVariables params t@(T_SingleQuoted id s) =
             || "perl" `isPrefixOf` commandName
             || isConcatenatedWithExpansion
 
-    commonlyQuoted = ["PS0", "PS1", "PS2", "PS3", "PS4", "PROMPT_COMMAND"]
+    commonlyQuoted = ["PS0", "PS1", "PS2", "PS3", "PS4", "PROMPT_COMMAND"] -- PS0 is bash 4.4+
     isOkAssignment t =
         case t of
             T_Assignment _ _ name _ _ -> name `elem` commonlyQuoted