Print line with leading whitespaces - mawk can't handle (E)RE correctly

[apt4user]

Version: mawk 1.3.4 20200120 Hi, mawk can't handle the following expressions:

echo " (4 x space) testtest" | awk '/^[[:space:]]{4}/ {print}' => prints nothing

echo " (4 x space) testtest" | awk '/^[\t]{4}/ {print}' => prints nothing

echo " (4 x space) testtest" | awk '/^[ \t]{4}/ {print}' => prints nothing

Greetings

[ThomasDickey]

This works for current versions of mawk.