Test Guzzle 7.0.0-beta1

Problem/Motivation

Guzzle 7 went into beta this week. https://github.com/guzzle/guzzle/releases/tag/7.0.0-beta.1

Proposed resolution

We should test this beta with Drupal 9 and determine if we are compatible with it in case Guzzle 7.0.0 is released before Drupal 9.

Remaining tasks

• Create a test patch that updates our core/composer.json requirement to the Guzzle 7 beta.
• Investigate any test failures, etc.

User interface changes

N/A

API changes

N/A

Data model changes

N/A

Release notes snippet

Needed. TBD.