Work around ThreadPool error when targeting HashLink in Haxe 4.0-4.1. #1273

Job	Run time
flash-samples	36s
air-samples (4.0.5)	3m 1s
air-samples (4.1.5)	3m 22s
html5-samples	1m 23s
air-samples (4.2.5)	3m 0s
android	25m 39s
docs	30s
air-samples (4.3.1)	3m 28s
ios	11m 53s
linux	14m 48s
macos	42m 49s
windows	15m 28s
package-haxelib	2m 12s
hashlinkc-samples (windows-latest)	1m 41s
hashlinkc-samples (ubuntu-20.04)	1m 35s
neko-samples (3.4.7, windows-latest)	47s
hashlink-samples (windows-latest)	48s
hashlinkc-samples (macos-12)	1m 39s
neko-samples (3.4.7, ubuntu-20.04)	15s
hashlink-samples (ubuntu-20.04)	27s
hashlink-samples (macos-12)	48s
neko-samples (3.4.7, macos-12)	44s
neko-samples (4.2.5, windows-latest)	40s
neko-samples (4.2.5, ubuntu-20.04)	17s
neko-samples (4.2.5, macos-12)	51s
notify	0s
	2h 18m 41s

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