Add support for version 26.3 in supported-versions.json

[dsnsgithub]

No description provided.

[github-actions]

The game launched and entered a survival singleplayer world with the HUD active, on every supported Minecraft version, for 6c7122f. A ❌ means that version's launch test did not produce a screenshot — check its job. Title-screen screenshots and game logs are in the run artifacts.

1.21	1.21.1	1.21.2	1.21.3
1.21.4	1.21.5	1.21.6	1.21.7
1.21.8	1.21.9	1.21.10	1.21.11
26.1	26.1.1	26.1.2	26.2
26.3 ❌ no screenshot

[dsnsgithub]

The existing 26.2 jar works for 26.3.