Bump CI Unity LTS to 6000.3.24f1

[Sebastien Lebreton (sailro)]

Updates the CI Unity Editor pin from 6000.3.23f1 to 6000.3.24f1 and updates the matching changeset used by the Linux, macOS, and Windows installer URLs.

Validation:

• Confirmed 6000.3.24f1 is the latest Unity 6.3 LTS patch.
• Confirmed all three CI installer URLs are available.

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