Drop linux/arm (32-bit) support #1336

Job	Run time
build.20-true	16m 7s
build.22-true	14m 8s
build.20-false	4m 22s
build.22-false	4m 21s
unit.heroku-20.buildpack-clojure	3m 41s
unit.heroku-22.buildpack-clojure	3m 40s
unit.heroku-20.buildpack-go	3m 28s
unit.heroku-22.buildpack-go	3m 1s
unit.heroku-20.buildpack-gradle	3m 23s
unit.heroku-22.buildpack-gradle	3m 30s
unit.heroku-20.buildpack-java	3m 33s
unit.heroku-22.buildpack-java	3m 1s
unit.heroku-20.buildpack-multi	3m 51s
unit.heroku-22.buildpack-multi	4m 5s
unit.heroku-20.buildpack-nodejs	3m 16s
unit.heroku-22.buildpack-nodejs	3m 36s
unit.heroku-20.buildpack-null	3m 22s
unit.heroku-22.buildpack-null	3m 0s
unit.heroku-20.buildpack-php	3m 18s
unit.heroku-22.buildpack-php	3m 32s
unit.heroku-20.buildpack-play	4m 17s
unit.heroku-22.buildpack-play	4m 3s
unit.heroku-20.buildpack-python	4m 43s
unit.heroku-22.buildpack-python	4m 0s
unit.heroku-20.buildpack-ruby	3m 45s
unit.heroku-22.buildpack-ruby	3m 56s
unit.heroku-20.buildpack-scala	4m 23s
unit.heroku-22.buildpack-scala	3m 51s
unit.heroku-20.buildpack-static	4m 16s
unit.heroku-22.buildpack-static	3m 39s
	2h 15m 8s

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