Add Sourcegraph ignore file #21214

Job	Run time
LP64-WIP	3m 32s
build-windows (imx8 imx8x imx8m imx8ulp)	9m 33s
build-windows (-d, lnl)	6m 36s
build-windows (tgl tgl-h)	8m 2s
manifest-check	47s
build-windows (mtl lnl)	7m 39s
build-linux (mnfst, ptl)	4m 24s
build-linux (mnfst, imx8 imx8x imx8m imx8ulp)	6m 34s
build-windows (ptl)	6m 29s
build-linux (zmain, ptl)	4m 28s
build-linux (mnfst, mtl lnl)	5m 18s
build-linux (zmain, mtl lnl)	5m 40s
build-linux (mnfst, --all)	16m 12s
build-linux (mnfst, tgl tgl-h)	5m 0s
build-linux (zmain, imx8 imx8x imx8m imx8ulp)	6m 17s
build-linux (-d, mnfst, lnl)	4m 15s
build-linux (zmain, tgl tgl-h)	5m 18s
compare-linux-win	1m 22s
	1h 47m 26s

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