fix(forms): Fix a minor error: pendingValue is a value, not a boolean flag.

[dylhunn]

Fix a minor error: pendingValue is a value, not a boolean flag.

The bug should have no effect since it's a typings-only, internal-only bug, but it's good to fix nonetheless.

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.io application / infrastructure changes
• Other... Please describe:

What is the current behavior?

_pendingValue has the wrong type. This is an internal-only type with no consequences.

Issue Number: N/A

What is the new behavior?

_pendingValue has the right type (any).

Does this PR introduce a breaking change?

• Yes
• No

Other information

[jessicajaniuk]

LGTM 🍪

[dylhunn]

Running presubmit: http://test/OCL:416066118:BASE:416066148:1639417585696:e732db0f

[alxhub]

This PR was merged into the repository by commit 815d4ce.

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