Re-enable previously disabled aarch64 tests

[jtattermusch]

Based on #8126 (only the last commit is the actual change).

My experiments show that after upgrading netty-tcnative-boringssl-static, the tests are reasonably stable (i got a few consecutive passing runs).

[jtattermusch]

@ejona86

[ejona86]

There's more to the tcnative upgrade process than this. In particular right now, tcnative 2.0.35 is incompatible with static JNI builds as used internally because it swapped to netty-jni-util which was incompatible for a while: netty/netty-jni-util#5. @dapengzhang0 was going to be upgrading Netty this quarter, which entails dealing with the new netty-jni-util stuff and jumping over the incompatible versions.

[jtattermusch]

Fair enough, thanks for the clarification.
I removed the netty-tcnative-boringssl-static upgrade part and only left the part that reenables the tests.
They can be re-enabled once netty-tcnative-boringssl-static is upgraded.

@dapengzhang0 do you have an ETA for the netty-tcnative-boringssl-static upgrade?

[ejona86]

#8167 bumped the version of Netty. So this may be ready.

[jtattermusch]

I rebased and started an adhoc run

[jtattermusch]

@ejona86 the adhoc run is green, so this PR should be safe to merge.