fix: Add LTS 2026 feed URLs.

[shichen85]

No description provided.

[adam-coster]

There are probably lots of other places in the code that do stuff depending on which channel is being used -- did you already make sure that this change completely gives you what you need? Does it result in installs to new locations we'll need to deal with? Should we expect that we'll have a growing number of alternate feeds as new LTSes get released?

My hunch is that we'll need a much more thorough set of changes than this to accommodate the new LTS feed, so we should probably sit down and figure out all of the ways it impacts things. What's the priority on this?

[shichen85]

Indeed, the LTS 2026 version has its own installation path and appdata path, so we will have to factor those in for the other Stitch functions.

The priority is low on this one, as it only breaks the GitHub Action igor-setup if the user wants to infer the runtime from the yyp file. The workaround is to explicitly define the runtime version.