Update RobotFramework to 6.x

[php-coder]

Changelogs:

• https://github.com/robotframework/robotframework/releases/tag/v6.0rc1
• https://github.com/robotframework/robotframework/releases/tag/v6.0rc2
• https://github.com/robotframework/robotframework/releases/tag/v6.0
• https://github.com/robotframework/robotframework/releases/tag/v6.0.1
• https://github.com/robotframework/robotframework/releases/tag/v6.0.2
• https://github.com/robotframework/robotframework/releases/tag/v6.1a1
• https://github.com/robotframework/robotframework/releases/tag/v6.1b1
• https://github.com/robotframework/robotframework/releases/tag/v6.1rc1
• https://github.com/robotframework/robotframework/releases/tag/v6.1
• https://github.com/robotframework/robotframework/releases/tag/v6.1.1

Blocked by: #1571