tree-wide: use IN_SET macro (#6977)

src/basic/utf8.c

@@ -73,7 +73,7 @@ static bool unichar_is_control(char32_t ch) {
           '\t' is in C0 range, but more or less harmless and commonly used.
         */
 
-        return (ch < ' ' && ch != '\t' && ch != '\n') ||
+        return (ch < ' ' && !IN_SET(ch, '\t', '\n')) ||
                 (0x7F <= ch && ch <= 0x9F);
 }