fix(mv3): use correct file paths in mv3 test builds

[danjm]

Description

Prior to this PR, yarn start:test:mv3 would fail. The error was:

The problem was introduced in #23672

That PR has the following in the description:

...The manifest file sometimes references files using a path relative to both the repo and the bundled extension (background.html and popup.html) and sometimes it doesn't (inpage.js lives in the scripts folder).
This PR makes the paths relative to the repo (and the bundled extension).

The problem is that there were two instances of the file paths that were not updated. Those instances only applied to mv3 test builds. This PR updates those instances.

Related issues

Fixes: https://github.com/MetaMask/MetaMask-planning/issues/2378

Manual testing steps

1. yarn start:test:mv3 should successfully create a build

Pre-merge author checklist

• I’ve followed MetaMask Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[metamaskbot]

Builds ready [4617a26]

• builds: chrome, firefox
• builds (beta): chrome
• builds (flask): chrome, firefox
• builds (MMI): chrome, firefox
• builds (test): chrome, firefox
• builds (test-flask): chrome, firefox
• build viz: Build System
• mv3: Background Module Init Stats
• mv3: UI Init Stats
• mv3: Module Load Stats
• mv3: Bundle Size Stats
• mv2: E2e Actions Stats
• code coverage: Report
• storybook: Storybook
• typescript migration: Dashboard
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5, 6
  • common: 0, 1, 2, 3, 4, 5, 6, 7, 8
  • content-script: 0
  • ui: 0, 1, 10, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (1189 ± 654 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	58	288	125	54	26
		domContentLoaded	9	63	23	15	7
		load	46	3296	1189	1362	654
		domInteractive	9	63	23	15	7

Bundle size diffs

• background: 0 Bytes (0.00%)
• ui: 0 Bytes (0.00%)
• common: 0 Bytes (0.00%)