Fixes https://github.com/denoland/deno/issues/29707.
Not particularly happy with this one, but the only other idea I had was
to just ignore errors about non-existent exports when we build the graph
for a top level install. That might end up being the best solution.
For background, when you do a top level install that includes a jsr
dependency, we fetch the exports for the jsr package and then use those
exports as roots in the module graph (which triggers caching those
files).
To find those exports correctly, we need to know what version will end
up being cached, otherwise we may end up trying to reference exports
that don't exist on the actual package.
Previously, we could just look up the version in the lockfile and that
worked, but it turns out that was depending on the behavior that was
reverted in https://github.com/denoland/deno/pull/29642.
