stable9 is not compatible with PHP 7.1

[ghost]

Description

See: #26431

Related Issue

See: #26431

Motivation and Context

See: #26431

How Has This Been Tested?

Not tested due to the lack of a PHP 7.1 install But its just copy'n'paste from the PHP7.0 check of stable8.2 with the proper change for PHP7.1

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[mention-bot]

@RealRancor, thanks for your PR! By analyzing the history of the files in this pull request, we identified @owncloud-bot, @LukasReschke and @butonic to be potential reviewers.

[DeepDiver1975]

👍