Fix compute matrix dropping trailing zeros

[jrhemstad]

Description

The compute-matrix script would process every value through jq -c . to ensure the output was "compact". However, this had the effect of processing some values as numbers which caused problems, e.g., it would drop a trailing zero in the devcontainer_version: 23.10.

Instead, just specify -c on every jq query to ensure compact output.

Checklist

• New or existing tests cover these changes.
• The documentation is up to date with these changes.