Fixes #36997 - Use selenium_chrome_headless for integration tests #175

Job	Run time
Setup matrix	4s
Setup matrix	4s
Rubocop	1m 9s
Rubocop	1m 9s
test:units - Ruby 2.7 and Node 14 on PostgreSQL 12	9m 22s
test:units - Ruby 2.7 and Node 14 on PostgreSQL 12	9m 22s
test:functionals - Ruby 2.7 and Node 14 on PostgreSQL 12	7m 54s
test:functionals - Ruby 2.7 and Node 14 on PostgreSQL 12	7m 54s
test:graphql - Ruby 2.7 and Node 14 on PostgreSQL 12	2m 4s
test:graphql - Ruby 2.7 and Node 14 on PostgreSQL 12	2m 4s
webpack:compile test:integration - Ruby 2.7 and Node 14 on PostgreSQL 12	8m 27s
webpack:compile test:integration - Ruby 2.7 and Node 14 on PostgreSQL 12	8m 17s
db:seed - Ruby 2.7 and Node 14 on PostgreSQL 12	1m 35s
db:seed - Ruby 2.7 and Node 14 on PostgreSQL 12	1m 35s
assets:precompile RAILS_ENV=production DATABASE_URL=nulldb://nohost - Ruby 2.7 and Node 14 on PostgreSQL 12	3m 3s
assets:precompile RAILS_ENV=production DATABASE_URL=nulldb://nohost - Ruby 2.7 and Node 14 on PostgreSQL 12	3m 3s
Test suite	0s
Test suite	0s
	1h 7m 6s

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