matrix: Advertise video size properly when sharing the attachment #466

Job	Run time
golangci-lint	2m 28s
test (1.24.x)	1m 45s
test (stable)	1m 57s
build-upload (amd64, windows, windows)	1m 23s
build-upload (amd64, linux, linux)	1m 31s
build-upload (amd64, mac, darwin)	1m 24s
	10m 28s

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