[nrf fromlist] tests: arch: common: interrupt: Add missing volatile keyword

Variable test_vector was missing volatile keyword and test was failing
on some targets when LTO was enabled (could also failed without LTO).

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>

Upstream PR #: 109119

Author: nordic-krch

tests/arch/common/interrupt/src/test_shared_irq.h

@@ -29,7 +29,7 @@ static inline void name(const void *data)		\
 	test_vector[idx] = result_vector[idx];		\
 }							\
 
-static uint32_t test_vector[TEST_VECTOR_SIZE] = {
+static volatile uint32_t test_vector[TEST_VECTOR_SIZE] = {
 };
 
 static uint32_t result_vector[TEST_VECTOR_SIZE] = {