Prevent CI from running twice on PRs #361

Job	Run time
Lint	36s
[email protected]	1m 12s
[email protected]	1m 9s
[email protected]	1m 4s
[email protected]	1m 5s
typescript@next	1m 13s
Floating Dependencies (ubuntu-latest, chrome)	49s
Floating Dependencies (ubuntu-latest, firefox)	51s
Tests (ubuntu-latest, chrome, 16)	42s
Tests (ubuntu-latest, chrome, 18)	50s
Tests (ubuntu-latest, firefox, 16)	58s
Tests (ubuntu-latest, firefox, 18)	51s
Docs app	50s
Tests - ember-lts-3.28	56s
Tests - ember-lts-4.4	1m 1s
Tests - ember-lts-4.12	1m 2s
Tests - ember-release	1m 0s
Tests - ember-beta	1m 10s
Tests - ember-classic	1m 9s
Tests - embroider-safe	1m 9s
Tests - embroider-optimized	1m 13s
Tests - ember-canary	58s
	21m 48s

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