[SKIP SOF-TEST] rebuild-testbench.sh: cosmetic improvements #15981

Job	Run time
manifest-check	40s
build-linux (mnfst, imx8 imx8x imx8m)	4m 11s
build-windows (imx8 imx8x imx8m)	8m 4s
build-linux (mnfst, mtl)	3m 57s
build-windows (mtl)	5m 55s
LP64-WIP	3m 27s
build-linux (mnfst, lnl)	3m 58s
build-windows (tgl tgl-h)	7m 8s
build-linux (mnfst, tgl tgl-h)	5m 0s
build-windows (-d, mtl)	5m 44s
build-linux (zmain, imx8 imx8x imx8m)	4m 21s
build-linux (zmain, mtl)	4m 9s
build-linux (zmain, lnl)	3m 49s
build-linux (zmain, tgl tgl-h)	4m 52s
build-linux (-d, mnfst, mtl)	3m 58s
compare-linux-win	39s
	1h 9m 52s

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