tests/pkg_heatshrink: re-enable CI test

When moved out of `unittests` running test on CI was not re-enabled.

tests/pkg_heatshrink/Makefile

@@ -5,6 +5,8 @@ BOARD_INSUFFICIENT_MEMORY := arduino-duemilanove \
                              nucleo-f031k6 \
                              #
 
+TEST_ON_CI_WHITELIST += all
+
 USEPKG += heatshrink
 USEMODULE += embunit