Missing `swift`- prefix from SDKs

[svanimpe]

I struggled a bit getting carton sdk install to work.

My first guess was to try carton sdk install 5.8, which didn't work. I then tried a tag name, for example: carton sdk install swift-wasm-5.9-SNAPSHOT-2023-08-01-a but that didn't work either.

I took me a while to figure out that I need to drop the swift- prefix from the tags. Is there a reason this is required, or is it a bug?

[kateinoigakukun]

The version specifier used by carton sdk install follows the .swift-version file conversion used in swiftenv. This design was intentional, but I understand it's not the ideal situation. We can consider better diagnostics.