PSA: updating Nearform 10.15 test macs

[AshCripps]

Going to be updating the nearform 10.15 macs to version 10.15.4 - this patch should contain the fix for nodejs/node#30030 and also unblock nodejs/node#32489.

Ill stagger the updates, only doing one at time so we can still run CI.

[AshCripps]

test-macstadium-macos10.15-x64-1 updated. test build - https://ci.nodejs.org/job/node-test-commit-osx/32969/nodes=osx1015/

EDIT: seems xcodes gone missing

[AshCripps]

Xcode went walkies, a reinstall brought it back: https://ci.nodejs.org/job/node-test-commit-osx-AshCripps/10/nodes=test-nearform-macos10.15-x64-1/console is now building, waiting for the tests to pass before moving on.

EDIT: build passed but it is still yellow because of test.sequential/test-timers-blocking-callback which I think is a known flake

[AshCripps]

All machines upto date seeing green builds too 🎉 https://ci.nodejs.org/job/node-test-commit-osx/nodes=osx1015/