tests: kernel: tickless: Don't run on nucleo_l073rz

Tickless test enables PM which implies use of LPTIM as ticker on STM32
platforms.
Specifically on nucleo_l073rz, this configuration is fragile as only
LSI(37KHz) could be used as LPTIM tick source, whith a huge accuracy
tolerance (20%).
This works on most cases, when a specific tick freq (4000 ticks/sec),
but this tests explicitly requires tick frequency set to 100.

Excludes nucleo_l073rz for this test.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>