tools: document that nixpkgs updates should not be backported · nodejs/node@d09ba98

Original file line number	Diff line number	Diff line change
`@@ -193,7 +193,10 @@ jobs:`
`193`	`193`	`rm temp-output`
`194`	`194`	`- id: nixpkgs-unstable`
`195`	`195`	`subsystem: tools`
`196`		`-label: tools`
	`196`	`+# dont-land labels are there so we can guarantee released versions of`
	`197`	`+# Node.js can be built with the same env along the whole release line life – or`
	`198`	`+# at least we can detect and document necessary updates.`
	`199`	`+label: tools, dont-land-on-v20.x, dont-land-on-v22.x, dont-land-on-v24.x, dont-land-on-v25.x`
`197`	`200`	`run: \|`
`198`	`201`	`./tools/dep_updaters/update-nixpkgs-pin.sh > temp-output`
`199`	`202`	`cat temp-output`