fix(document-ai): Downgrade p-queue package for CommonJS compatibility

[angelcaamal]

Description

This PR downgrades p-queue from ^8.0.0 to ^6.6.2. The version 8.0.0 is a pure ESM package, which is incompatible with our current CommonJS (require()) environment and caused ERR_REQUIRE_ESM errors during execution.

Changes

package.json

• Downgraded p-queue from ^8.0.0 to ^6.6.2 to ensure compatibility with require().
  Fixes #

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Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• Tests pass: npm test (see Testing)
• Lint pass: npm run lint (see Style)
• Required CI tests pass (see CI testing)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This pull request is from a branch created directly off of GoogleCloudPlatform/nodejs-docs-samples. Not a fork.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new sample directory, and I created GitHub Actions workflow for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

Note: Any check with (dev), (experimental), or (legacy) can be ignored and should not block your PR from merging (see CI testing).

[gemini-code-assist]

Code Review

This pull request downgrades the p-queue dependency in document-ai/package.json from version ^8.0.0 to ^6.6.2. There are no review comments, and I have no feedback to provide.

[Kef131]

LGTM