Fix: vitest-pool-workers use env in .dev.vars

[Skye-31]

What this PR solves / how to test

#5612 added support for selecting the environment of config used, but it missed passing it to the code that reads .dev.vars.{environment}

Fixes #5641

Author has addressed the following

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• E2E Tests CI Job required? (Use "e2e" label or ask maintainer to run separately)
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• Changeset (Changeset guidelines)
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• Public documentation
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[changeset-bot]

🦋 Changeset detected

Latest commit: bb7a6ba

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
wrangler	Patch
@cloudflare/vitest-pool-workers	Patch

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[threepointone]

approving pending CI, thanks!

[github-actions]

A wrangler prerelease is available for testing. You can install this latest build in your project with:

npm install --save-dev https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9759525158/npm-package-wrangler-6180

You can reference the automatically updated head of this PR with:

npm install --save-dev https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/prs/6180/npm-package-wrangler-6180

Or you can use npx with this latest build directly:

npx https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9759525158/npm-package-wrangler-6180 dev path/to/script.js

Additional artifacts:

npx https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9759525158/npm-package-create-cloudflare-6180 --no-auto-update

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9759525158/npm-package-cloudflare-kv-asset-handler-6180

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9759525158/npm-package-miniflare-6180

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9759525158/npm-package-cloudflare-pages-shared-6180

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9759525158/npm-package-cloudflare-vitest-pool-workers-6180

Note that these links will no longer work once the GitHub Actions artifact expires.

---

wrangler@3.62.0 includes the following runtime dependencies:

Package	Constraint	Resolved
miniflare	workspace:*	3.20240620.0
workerd	1.20240620.1	1.20240620.1
workerd --version	1.20240620.1	2024-06-20

Please ensure constraints are pinned, and miniflare/workerd minor versions match.