Revert "tests: ram_context_for_isr: exclude STM32C0 boards"

This reverts commit 4f18ccd7
now that STM32C0 based target are supported by the test default
configuration (see commit 7dbd6001 ("tests: ram_context_for_isr:
Use Kconfig for IRQ config").

Signed-off-by: Etienne Carriere <etienne.carriere@st.com>