github: rename matrix to environment #104

Job	Run time
setup-matrix	13s
test (ubuntu-latest, accounting)	1m 53s
test (ubuntu-latest, auth)	3m 23s
test (ubuntu-latest, b2b)	4m 18s
test (ubuntu-latest, dialog)	3m 11s
test (ubuntu-latest, permissions)	1m 16s
test (ubuntu-latest, presence)	1m 0s
test (ubuntu-latest, record-route)	56s
test (ubuntu-latest, registration)	4m 12s
test (ubuntu-latest, startup)	1m 35s
test (ubuntu-latest, stir-shaken)	4m 28s
test (ubuntu-latest, topology-hiding)	3m 50s
test (ubuntu-latest, uac-auth)	2m 57s
	33m 12s

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