spacetimedb-update self-install fails if the install fails.

[bfops]

Description of Changes

Prior to this PR, when the call to upgrade (which installs the latest version) failed, self-install would print the error and then go on to print a success message.

This PR updates the logic so that we fail if the version installation fails.

Previous behavior:

The SpacetimeDB command line tool will now be installed into /var/folders/qn/7t0vq3ts721cmgt0tgrtgzl80000gn/T/tmp.OEcKoBCvjL
Downloading latest version...
Error: failed to download and install latest SpacetimeDB version: Could not fetch release info: HTTP status client error (403 Forbidden) for url (https://api.github.com/repos/clockworklabs/SpacetimeDB/releases/latest)

The `spacetime` command has been installed as /var/folders/qn/7t0vq3ts721cmgt0tgrtgzl80000gn/T/tmp.OEcKoBCvjL/spacetime

The install process is complete; check out our quickstart guide to get started!
	<https://spacetimedb.com/docs/getting-started>

New behavior:

The SpacetimeDB command line tool will now be installed into /var/folders/qn/7t0vq3ts721cmgt0tgrtgzl80000gn/T/tmp.b0ab4mKN8T
Downloading latest version...
Error: failed to download and install latest SpacetimeDB version

Caused by:
    0: Could not fetch release info
    1: HTTP status client error (403 Forbidden) for url (https://api.github.com/repos/clockworklabs/SpacetimeDB/releases/latest)

API and ABI breaking changes

No API/ABI breaking changes.

Expected complexity level and risk

1

Testing

• The installer now exits after saying "failed to download and install latest SpacetimeDB version", rather than continuing to a success message.

[coolreader18]

Yeah, that's fair. LGTM

[bfops]

Okay cool, thank you!