Update pnpm to v9.15.0 #1199

Job	Run time
Lints	1m 8s
Test ember-scoped-css	1m 4s
Test test-apps/classic-app	1m 48s
Test test-apps/embroider-app	1m 19s
Test test-apps/pods-embroider-app	1m 10s
Test test-apps/pods-classic-app	1m 33s
Floating ember-scoped-css	56s
ember-lts-4.4	2m 10s
Floating test-apps/classic-app	2m 4s
ember-lts-4.12	2m 3s
Floating test-apps/embroider-app	1m 16s
ember-lts-5.4	2m 17s
Floating test-apps/pods-embroider-app	1m 8s
ember-lts-5.8	1m 59s
Floating test-apps/pods-classic-app	1m 26s
ember-release	2m 8s
ember-beta	2m 2s
	27m 31s

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