Update dependency ember-source to v5.8.0 #1304

Job	Run time
lint	1m 1s
test against additional browser in BrowserStack	2m 9s
test bundlesize	1m 54s
Test php backend (7.2)	13s
test against Chrome	2m 27s
Test php backend (7.3)	13s
test CSP in .htaccess	1m 2s
test against Firefox	2m 33s
Test php backend (7.4)	16s
Test php backend (8.0)	14s
Test php backend (8.1)	20s
Test php backend (8.2)	14s
Test php backend (8.3)	19s
	12m 55s

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