Flow Bugfix Release: 8.3.16, 9.0.3

[markusguenther (Markus Günther)]

We tagged bugfix releases for Flow.
Thanks to all the contributors who helped with this release <3

• Marc Henry Schultz
• Karsten Dambekalns
• Denny Lubitz

The following fixes are included in the new version 8.3.16 and 9.0.3:

• TASK: Tweak Core\Bootstrap
• TASK: Improve PHP-check error message
• BUGFIX: Handle stand-alone format for weekdays

The following fixes are included in the new version 9.0.3:

• TASK: Remove experimental action
• BUGFIX: Prevent truncateArrayAtDepth(): Argument #1 ($array) must
• TASK: Resolve StyleCI