Fix main frontend validation (#6361)

# Description of Changes
#6312 reformatted `tauri.conf.json` via the Gradle script, which
reformats the entire file to not match the Prettier style. This PR
reformats the file back to Prettier format and changes the script to
update the version number without reformatting the entire file.

To be honest I'm not a huge fan of updating the version number with
regexes but it'd be a fool's errand to try and get Gradle to output JSON
in Prettier format, and this seems simpler than shelling out to run
Prettier over the file after the version string has been updated. Any
better ideas, let me know.