Upgrade Unity versions used to run tests on CI (Unity 6.3)

[nowsprinting]

No description provided.

[Copilot]

Pull request overview

This PR upgrades the Unity versions used for CI testing to newer releases, including the latest Unity 6.3 version. The changes ensure the project is tested against the most recent stable Unity versions across multiple release tracks.

• Updated four Unity versions across different release tracks (2019 LTS, 2022 LTS, Unity 6.0, and Unity 6.3)
• Consistently updated all matrix references to use the new Unity 6.3 version (6000.3.2f1)

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[github-actions]

Code Metrics Report

	master (0afe983)	#287 (35e1426)	+/-
Coverage	89.1%	89.1%	0.0%
Code to Test Ratio	1:1.3	1:1.3	0.0
Test Execution Time	11m17s	12m28s	+1m11s

Details

  |                     | master (0afe983) | #287 (35e1426) |  +/-   |
  |---------------------|------------------|----------------|--------|
  | Coverage            |            89.1% |          89.1% |   0.0% |
  |   Files             |               71 |             71 |      0 |
  |   Lines             |             2591 |           2591 |      0 |
  |   Covered           |             2309 |           2309 |      0 |
  | Code to Test Ratio  |            1:1.3 |          1:1.3 |    0.0 |
  |   Code              |             4628 |           4628 |      0 |
  |   Test              |             6186 |           6186 |      0 |
- | Test Execution Time |           11m17s |         12m28s | +1m11s |

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Reported by octocov