steam: add 32-bit mesa gl bits #590

Job	Run time
base / docker	22s
base-app / docker	32s
apps (retroarch, linux/amd64) / docker	34s
apps (firefox, linux/amd64) / docker	28s
apps (pulseaudio, linux/amd64) / docker	32s
apps (es-de, linux/amd64) / docker	38s
apps (sunshine, linux/amd64) / docker	26s
apps (xorg, linux/amd64) / docker	19s
apps (udevd, linux/amd64) / docker	18s
apps (steam, linux/amd64) / docker	39s
	4m 48s

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