Ignore missingType.iterableValue errors from PHPStan

[daledupreez]

Changes proposed in this Pull Request:

This PR adds missingType.iterableValue errors to the list of errors that we want PHPStan to ignore completely. Loosely typed arrays are _everywhere_in WordPress and WooCommerce, so it feels like requiring typed arrays is overkill (at least for now). The PR also updates our PHPStan baseline file with the new configuration.

Testing instructions

Code review. Confirm that PHPStan analysis passes.

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• [N/A] Covered with tests (or have a good reason not to test in description ☝️)
• [N/A] Tested on mobile (or does not apply)

Changelog entry

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Changelog Entry Comment

Comment

This is a pretty limited change to our PHPStan configuration, which is not really relevant to anyone outside the development team.

Post merge

• Added testing instructions to the Release Testing Instructions wiki page (or does not apply)
• Added the needs docs label (or does not apply)
• Included this PR in the Release Thread scope (or does not apply)

[Mayisha]