Plugin versions not updating on /plugins and /plugins-installed...

[JodiB-TPR]

Description of the issue

I recently downgraded from v4.7.0 to v4.6 of GOV.UK Frontend and restarted my kit. However, the version shown on the plugins pages still shows v4.7.0.

Steps to reproduce the issue

1. In terminal on Mac, run npm install govuk-frontend@4.6
2. Watch as it runs and shows as successful:

   
   added 1 package, changed 1 package, and audited 537 packages in 1s

128 packages are looking for funding run npm fund for details

found 0 vulnerabilities

3. Restart Companion Kit (`Ctrl + C` then `npm run dev`)
4. Go to prototype in browser and refresh / hard refresh the /plugins and /plugins-installed pages
5. See no change in version displayed
<img width="1122" alt="Screen Shot 2023-09-22 at 11 20 59 AM" src="https://github.com/alphagov/govuk-prototype-kit/assets/74964198/916d6900-11f0-45ef-856d-0901964e167c">
<img width="1201" alt="Screen Shot 2023-09-22 at 11 21 40 AM" src="https://github.com/alphagov/govuk-prototype-kit/assets/74964198/f77cde66-d2e7-4c93-b306-20417d55fe48">

## Actual vs expected behaviour
<!-- What is happening vs what would you expect to happen instead? -->
I'd expect to see the version updated to reflect v4.6 and for there to be an "update available" message displayed.

## Environment (where applicable)
<!-- Details of your operating system, browser and the version of the GOV.UK Prototype Kit you’re using may help us to reproduce your issue. -->

- Operating system: macOS Monterey v12.6.9
- Browser: Chrome 
- Browser version: Version 117.0.5938.88 (Official Build) (x86_64)
- GOV.UK Prototype Kit version: 13.13.3

[BenSurgisonGDS]

I cannot reproduce this in the wild. I did the following steps to an older v13 prototype I had locally:

• Upgraded to the latest version of GOV.UK Prototype Kit (v13.3.3) from the plugins page
• Upgraded to the latest version of GOV.UK Front end (v4.7.0) from the plugins page
• Downgraded GOV.UK Frontend to v4.6.0 using the cli command stated in this issue npm install govuk-frontend@4.6
• Waited for the prototype to restart in the terminal (I could have restarted it manually, but either case would have worked)
• Refreshed the plugins page (note this does not happen automatically, it never has and is not a bug)
• The plugins page now shows GOV.UK Frontend as version v4.6.0 as expected

[oli-rose28]

I've repeated all of the above steps on my Mac and it still works as expected.