style: grammar and style fixes in shields.json

[RobbieNeko]

Checklist

Required

• I wrote the PR title in conventional commit format.
• I ran the code formatter.
• I linked any relevant issues using github keyword syntax so it can be closed automatically.
• I have committed my changes to new branch that isn't main so it won't cause conflict when updating main branch later.

Purpose of change

Fixes #5680 and a couple other minor bits I noticed while looking

Describe the solution

An -> A
Remove a couple errant commas (comma splices I think)

Describe alternatives you've considered

• Accumulate more grammar fixes first
• Wait for Zchris or ProxieHunter to come back

Testing

Eyeballs confirmed that it's indeed English

Additional context

Smol PRs to close easy issues go brr

[ZChris13]

I will figure out how to use this thing eventually it's just low on the priority list

[scarf005]

@ZChris13 pull requests are for game development. let's keep the game talk on discord, thanks.