Fix '-rules' depreciation message

The message was instructing to use the "--rules" switch which doesn't exist.

Author: HugoGGuerrier

lkql_checker/src/gnatcheck-projects.adb

@@ -1214,7 +1214,7 @@ package body Gnatcheck.Projects is
             if not Rules_Depreciation_Emitted then
                Error_In_Tty
                  ("The '-rules' section is now deprecated. You should only " &
-                  "use the '--rules' and '--rule-file' command-line options.");
+                  "use the '--rule' and '--rule-file' command-line options.");
                Error_In_Tty
                  ("You can use the '--emit-lkql-rule-file' flag to " &
                   "automatically translate your rule configuration to the " &

testsuite/tests/gnatcheck/rules_depreciation_message/test.out

@@ -1,3 +1,3 @@
-gnatcheck: The '-rules' section is now deprecated. You should only use the '--rules' and '--rule-file' command-line options.
+gnatcheck: The '-rules' section is now deprecated. You should only use the '--rule' and '--rule-file' command-line options.
 gnatcheck: You can use the '--emit-lkql-rule-file' flag to automatically translate your rule configuration to the new LKQL format.
 main.adb:3:04: goto statement