fix(upload): ensure only image files are read for preview #12772

Job	Run time
changes	7s
core-build	1m 18s
templates	0s
tests (mongoose)	6m 49s
tests-e2e (1/8)	1m 25s
tests (postgres)	4m 28s
build-packages (db-mongodb)	32s
plugins (create-payload-app)	16s
tests (postgres-custom-schema)	4m 24s
tests-e2e (2/8)	2m 53s
build-packages (db-postgres)	29s
plugins (plugin-cloud)	40s
tests (postgres-uuid)	4m 23s
tests-e2e (3/8)	2m 9s
build-packages (bundler-webpack)	35s
plugins (plugin-cloud-storage)	34s
tests (supabase)	6m 21s
tests-e2e (4/8)	5m 47s
plugins (plugin-form-builder)	27s
build-packages (bundler-vite)	28s
tests-e2e (5/8)	1m 50s
build-packages (richtext-slate)	28s
plugins (plugin-nested-docs)	28s
tests-e2e (6/8)	1m 26s
build-packages (richtext-lexical)	29s
plugins (plugin-search)	32s
tests-type-generation	25s
build-packages (live-preview)	27s
plugins (plugin-sentry)	37s
build-packages (live-preview-react)	32s
tests-e2e (7/8)	2m 23s
plugins (plugin-seo)	33s
tests-e2e (8/8)	1m 41s
	55m 56s

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