Drop support for Safari < 15.6 #9786

Job	Run time
Linting	1m 13s
Basic Test	1m 34s
Type Checking (current version)	43s
Type Checking (other supported versions) (4.9)	1m 0s
Type Checking (other supported versions) (5.0)	1m 7s
Type Checking (other supported versions) (5.1)	1m 7s
Type Checking (other supported versions) (5.2)	1m 1s
Type Checking (other supported versions) (5.3)	1m 5s
Blueprint Tests	8m 0s
Node.js Tests	54s
Browserstack Tests (Safari, Edge)	3m 22s
All deprecations enabled	1m 27s
All deprecations enabled, with optional features	1m 28s
Deprecations as errors	1m 21s
Browser Tests (Firefox)	1m 42s
Smoke tests (Full Ember Apps) (classic-basics)	1m 22s
Deprecations as errors, with optional features	1m 30s
Smoke tests (Full Ember Apps) (embroider-basics)	1m 22s
Production build	1m 24s
Production build, with optional features	1m 25s
Publish channel to s3	0s
Publish alpha from default branch	0s
Deploy tags to npm	0s
Notify Discord	0s
	34m 7s

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