Update FilamentChange.py

[GregValiant]

Description

Add multi-line insertions.

This fixes... OR This improves... -->
Makes it possible to insert multiple lines of gcode before and after the M600.

Type of change

• [X ] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• [ X] Cura 4.x and 5.x

Test Configuration:

• Operating System: aawin10 and Marlin

Checklist:

• [ X] My code follows the style guidelines of this project as described in UltiMaker Meta and Cura QML best practices
• [ X] I have read the Contribution guide
• [ X] I have commented my code, particularly in hard-to-understand areas
• [X ] I have uploaded any files required to test this change