Group dependency update PRs in order to minimize the number of PRs to review.

Specify a PHP version in the Composer file to unblock PHP updates.

Readiness checklist

In order to have this pull request merged, complete the following tasks.

Pull request author tasks

• I checked that all workflows return a success.
• I included all the needed documentation for this change.
• I provided the necessary tests.
• I squashed all the commits into a single commit.
• I followed the
  Conventional Commit v1.0.0 spec.
• I wrote the necessary upgrade instructions in the
  upgrade guide.
• If this pull request is about and existing issue, I added the
  Fix #ISSUE_NUMBER or Close #ISSUE_NUMBER text to the description of
  the pull request.

Super-linter maintainer tasks

• Label as breaking if this change breaks compatibility with the previous
  released version.
• Label as either: automation, bug, documentation, enhancement,
  infrastructure.
• Add the pull request to a milestone, eventually creating one, that matches
  with the version that release-please proposes in the
  preview-release-notes CI job.