Set `GOTOOLCHAIN` to prevent go auto-upgrade #406

Job	Run time
Generate Jobs	1m 23s
1.21.1-bookworm	1m 0s
1.21.1-bullseye	1m 0s
1.21.1-alpine3.18	48s
1.21.1-alpine3.17	1m 33s
1.21.1-windowsservercore-ltsc2022, 1.21.1-nanoserver-ltsc2022	7m 22s
1.21.1-windowsservercore-1809, 1.21.1-nanoserver-1809	8m 45s
1.20.8-bookworm	1m 20s
1.20.8-bullseye	1m 13s
1.20.8-alpine3.18	3m 12s
1.20.8-alpine3.17	3m 38s
1.20.8-windowsservercore-ltsc2022, 1.20.8-nanoserver-ltsc2022	9m 37s
1.20.8-windowsservercore-1809, 1.20.8-nanoserver-1809	9m 13s
1.21.1-bookworm (force build)	4m 5s
1.21.1-bullseye (force build)	5m 21s
1.20.8-bookworm (force build)	3m 27s
1.20.8-bullseye (force build)	3m 41s
1.21.1-bookworm (i386)	1m 14s
1.21.1-bullseye (i386)	1m 4s
1.21.1-alpine3.18 (i386)	3m 12s
1.21.1-alpine3.17 (i386)	41s
1.20.8-bookworm (i386)	1m 15s
1.20.8-bullseye (i386)	3m 27s
1.20.8-alpine3.18 (i386)	4m 12s
1.20.8-alpine3.17 (i386)	3m 58s
	1h 25m 41s

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