Slow, unnecessary version check updates on unrelated command

[LilithHafner]

When installing channel 1.8, I don't want to check for updates to other channels. Especially not if that slows down the instillation of the channel I'm asking for.

In this case, the "Checking for new version" steps took longer than the "Installing" step.

$ julia +1.8
ERROR: `1.8` is not installed. Please run `juliaup add 1.8` to install channel or version.
$ juliaup add 1.8
Checking for new Julia versions
Checking for new version on channel 'pr55152' is taking a while... This can be slow due to server caching
Checking for new version on channel 'nightly' is taking a while... This can be slow due to server caching
Checking for new version on channel 'pr56882' is taking a while... This can be slow due to server caching
Checking for new version on channel 'pr56707' is taking a while... This can be slow due to server caching
Installing Julia 1.8.5+0.aarch64.linux.gnu

[LilithHafner]

Moments later, I tried to add version 1.7 and all these same channels were re-checked. This is impactful in the case of bisecting based on Julia version.