Append -gnu to RUBY_TARGET for GNU Linux builds (#511) #1878

Job	Run time
🔘 Static (3.2.2, ubuntu-latest, stable)	1m 59s
📥 Fetch CI data	3s
🧪 Test (2.7, ubuntu-latest, 1.65)	5m 40s
🧪 Test (2.7, ubuntu-latest, stable)	2m 55s
🧪 Test (2.7, macos-latest, stable)	3m 33s
🧪 Test (2.7, windows-2022, stable)	8m 29s
🧪 Test (3.0, ubuntu-latest, 1.65)	5m 18s
🧪 Test (3.0, ubuntu-latest, stable)	2m 41s
🧪 Test (3.0, macos-latest, stable)	1m 57s
🧪 Test (3.0, windows-2022, stable)	6m 51s
🧪 Test (3.1, ubuntu-latest, 1.65)	5m 16s
🧪 Test (3.1, ubuntu-latest, stable)	2m 36s
🧪 Test (3.1, windows-2022, stable)	7m 40s
🧪 Test (3.2, ubuntu-latest, 1.65)	5m 21s
🧪 Test (3.2, ubuntu-latest, stable)	2m 39s
🧪 Test (3.2, macos-latest, stable)	2m 37s
🧪 Test (3.2, windows-2022, stable)	7m 57s
🧪 Test (3.3, ubuntu-latest, 1.65)	5m 38s
🧪 Test (3.3, ubuntu-latest, stable)	2m 33s
🧪 Test (3.3, macos-latest, stable)	2m 16s
🧪 Test (3.3, windows-2022, stable)	8m 0s
🧪 Test (3.4, ubuntu-latest, 1.65)	5m 30s
🧪 Test (3.4, ubuntu-latest, stable)	2m 44s
🧪 Test (3.4, macos-latest, stable)	2m 13s
🧪 Test (truffleruby, ubuntu-latest, stable)	2m 27s
🧪 Test (truffleruby, macos-latest, stable)	2m 31s
🧪 Test (mswin, windows-2022, stable-x86_64-pc-windows-msvc)	4m 23s
	1h 51m 47s

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