Quote a keys for CritBitTree $ impl. Fixes #7987

Author: data-man

lib/pure/collections/critbits.nim

@@ -322,10 +322,14 @@ proc `$`*[T](c: CritBitTree[T]): string =
       const avgItemLen = 16
     result = newStringOfCap(c.count * avgItemLen)
     result.add("{")
-    for key, val in pairs(c):
-      if result.len > 1: result.add(", ")
-      result.add($key)
-      when T isnot void:
+    when T is void:
+      for key in keys(c):
+        if result.len > 1: result.add(", ")
+        result.addQuoted(key)
+    else:
+      for key, val in pairs(c):
+        if result.len > 1: result.add(", ")
+        result.addQuoted(key)
         result.add(": ")
         result.addQuoted(val)
     result.add("}")