chore: bump miniflare to 3.20230821.0

[mrbbot]

What this PR solves / how to test:

Hey! 👋 This PR bumps miniflare to 3.20230821.0. Whilst this won't cause major user facing changes on its own, it's a pre-requisite for #3726 and #3774.

Associated docs issue(s)/PR(s):

N/A

Author has included the following, where applicable:

• Tests
• Changeset (Changeset guidelines)

Reviewer is to perform the following, as applicable:

• Checked for inclusion of relevant tests
• Checked for inclusion of a relevant changeset
• Checked for creation of associated docs updates
• Manually pulled down the changes and spot-tested

Note for PR author:

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[changeset-bot]

🦋 Changeset detected

Latest commit: 8b639a9

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

This PR includes changesets to release 2 packages

Name	Type
@cloudflare/pages-shared	Minor
wrangler	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[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/5944538745/npm-package-wrangler-3799

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

npm install --save-dev https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/prs/5944538745/npm-package-wrangler-3799

Or you can use npx with this latest build directly:

npx https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/5944538745/npm-package-wrangler-3799 dev path/to/script.js

Additional artifacts:

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/5944538745/npm-package-cloudflare-pages-shared-3799

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

[codecov]

Codecov Report

Merging #3799 (0b303ec) into main (c053403) will increase coverage by 0.09%.
Report is 2 commits behind head on main.
The diff coverage is 66.66%.

❗ Current head 0b303ec differs from pull request most recent head d74e1ed. Consider uploading reports for the commit d74e1ed to get more accurate results

@@            Coverage Diff             @@
##             main    #3799      +/-   ##
==========================================
+ Coverage   75.26%   75.36%   +0.09%     
==========================================
  Files         195      195              
  Lines       11450    11430      -20     
  Branches     3020     3018       -2     
==========================================
- Hits         8618     8614       -4     
+ Misses       2832     2816      -16     

Files Changed	Coverage Δ
packages/wrangler/src/r2/index.ts	87.30% <66.66%> (ø)

... and 4 files with indirect coverage changes

[mrbbot]

Skipping this version bump. We'll bump miniflare once a version that depends on workerd with cloudflare/workerd#1077 has been released. 👍