Better regex escape (#2862)

Author: kddejong

src/cfnlint/template/transforms/_language_extensions.py

@@ -197,7 +197,7 @@ def _replace_string_params(
         if not re.search(pattern, s):
             return (True, s)
         for k, v in params.items():
-            s = re.sub(rf"\${{{k}}}", v, s)
+            s = re.sub(rf"\$\{{{k}\}}", v, s)
 
         return (not (bool(re.search(pattern, s))), s)