drop support for node < 18 #123

Job	Run time
Tests and Linting	1m 47s
Floating Dependencies	2m 9s
ember-canary - Allowed to fail	1m 10s
ember-try: ember-lts-3.16	2m 40s
ember-beta - Allowed to fail	1m 9s
ember-try: ember-lts-3.20	2m 38s
ember-release-no-deprecations - Allowed to fail	1m 14s
ember-try: ember-lts-3.24	2m 36s
ember-try: ember-lts-3.28	2m 40s
ember-try: ember-release	2m 7s
ember-try: ember-default-with-jquery	2m 43s
ember-try: ember-classic	2m 36s
ember-try: embroider-safe	2m 54s
ember-try: embroider-optimized	3m 4s
ember-try: no-deprecations	2m 41s
	34m 8s

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