related #22534; fixes documentation rendering of custom number literal routine declaration (#23015)

I'm not sure if this is a complete fix, as it does not match the
expected output given in the issue. The expected output given in the
issue highlights the identifier after the `'` the same color as numeric
literals (blue), and this change does not address that. I think that
would involve simplifying `nimNumberPostfix`.

However, this fixes the issue where the routine declaration was rendered
as a string.
New rendering: 
![Screenshot from 2023-11-30
22-17-17](https://github.com/nim-lang/Nim/assets/80008541/b604ce27-a4ad-496b-82c3-0b568d99a8bf)

lib/packages/docutils/highlite.nim

@@ -324,17 +324,18 @@ proc nimNextToken(g: var GeneralTokenizer, keywords: openArray[string] = @[]) =
       pos = nimNumber(g, pos)
     of '\'':
       inc(pos)
-      g.kind = gtCharLit
-      while true:
-        case g.buf[pos]
-        of '\0', '\r', '\n':
-          break
-        of '\'':
-          inc(pos)
-          break
-        of '\\':
-          inc(pos, 2)
-        else: inc(pos)
+      if g.kind != gtPunctuation:
+        g.kind = gtCharLit
+        while true:
+          case g.buf[pos]
+          of '\0', '\r', '\n':
+            break
+          of '\'':
+            inc(pos)
+            break
+          of '\\':
+            inc(pos, 2)
+          else: inc(pos)
     of '\"':
       inc(pos)
       if (g.buf[pos] == '\"') and (g.buf[pos + 1] == '\"'):