tests: counter: counter_basic_api: exclude nucleo_f302r8

Exclude nucleo_f302r8 platform as the tests doesn't fit in flash size.
This is due to that fact that we pull in newlib for the STM32 counter
driver.

Fixes #15460

Signed-off-by: Kumar Gala <[email protected]>

Author: galak

tests/drivers/counter/counter_basic_api/testcase.yaml

@@ -3,3 +3,4 @@ tests:
     tags: drivers
     depends_on: counter
     min_ram: 16
+    platform_exclude: nucleo_f302r8