Turn off optimization mode when compiling tests for K/N

[homuroll]

Optimization was turned on due to performance problems. However, with new K/N memory manager these performance problems seem to be fixed. On the other hand, compiling in optimized mode significantly increases the compiler's memory consumption, so it's better to turn it off.
In particular, we (in K/N team) are having some problems with updating to LLVM 16 due to increased memory consumption (it's still being investigated what causes it), more details here: https://youtrack.jetbrains.com/issue/KT-68418/Native-updating-to-LLVM-16-makes-kotlinx.coroutines-build-in-Aggregate-unstable. This commit workarounds it.

[qwwdfsad]

There is a tiny degradation in Native test times and compilation speed improvement.

Waiting for the stats from Igor and it's good to go

[homuroll]

Some numbers:

• 2nd run of ./gradlew clean :kotlinx-coroutines-core:linkDebugTestMacosArm64 sped up from ~69 sec to ~19 sec
• but the running time of the test binary increased from ~38 sec to ~49.5 sec

The difference between the optimized binary and the non-optimized one is noticeable but I believe it's not as bad as it used to be and won't be a problem.