Add Sourcegraph ignore file #21218

Job	Run time
manifest-check	48s
LP64-WIP	3m 44s
build-windows (mtl lnl)	7m 51s
build-windows (tgl tgl-h)	7m 31s
build-windows (ptl)	7m 13s
build-windows (-d, lnl)	7m 9s
build-linux (mnfst, imx8 imx8x imx8m imx8ulp)	6m 15s
build-windows (imx8 imx8x imx8m imx8ulp)	9m 56s
build-linux (mnfst, tgl tgl-h)	5m 1s
build-linux (mnfst, ptl)	4m 5s
build-linux (zmain, imx8 imx8x imx8m imx8ulp)	6m 15s
build-linux (mnfst, --all)	16m 17s
build-linux (zmain, tgl tgl-h)	5m 13s
build-linux (mnfst, mtl lnl)	5m 48s
build-linux (-d, mnfst, lnl)	4m 0s
build-linux (zmain, mtl lnl)	5m 38s
build-linux (zmain, ptl)	4m 30s
compare-linux-win	30s
	1h 47m 44s

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