Several improvements to the Dependabot configuration

[desrosj]

What?

This PR makes a handful of changes to the Dependabot file that is currently configured to prepare updates for the GitHub Actions ecosystem.

• A default cooldown period of 7 days is being added.
• The group configuration has been updated to only target minor and patch updates (major version updates will each get their own isolated pull request).
• The limitation for number of concurrent pull requests at a given time has been raised from 10 to 20 (there are currently 21 unique third-party GitHub Actions being used).

Why?

• The cooldown value helps to guard against scenarios where a dependency is updated too soon after initial release, which could possibly result in falling victim to a supply chain attack.
• When major releases are mixed in with minor and patch updates, major versions that require broader action to be taken before being merged often block minor and patch updates.

Use of AI Tools

None.

[Copilot]

Pull request overview

This PR updates the repository’s Dependabot configuration for the github-actions ecosystem to better control update timing and PR organization.

Changes:

• Increased the concurrent Dependabot PR limit from 10 to 20.
• Added a default 7-day cooldown window before opening PRs for newly released versions.
• Adjusted grouping to only include minor/patch updates (so major updates are isolated).

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[github-actions]

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Co-authored-by: desrosj <[email protected]>
Co-authored-by: johnbillion <[email protected]>

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[github-actions]

Flaky tests detected in 5cc9e09.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/26263469362
📝 Reported issues:

• [Flaky Test] Text blocks sync modifications between users #77329 in /test/e2e/specs/editor/collaboration/collaboration-block-gauntlet.spec.ts