Improve build number on releases action

[kacimiamine]

Since I saw build 153 released and the next one was 156, I went to fixing the build number logic. What I did is:

• Read the Minecraft version from gradle.properties.
• Fetch the latest build of that version using the downloads service.
• If the version doesn't have build, it will return 0.
• Increment the build by 1.

I tested it on bash since I can't really test the workflow, but the commands work as intended (tested with 26.3, 26.2 and 26.4 that doesn't exist so I can see it returns 0).

Also moved the step down since it needs checkout first to read the gradle.properties file.

[jpenilla]

Thanks, but we considered this and several other alternatives before settling on the current implementation. This breaks several of the guarantees the current setup provides, especially around build races and retries/reruns. We will look into the skipped build numbers. We do not cancel in-progress overlapping builds, but it seems that multiple builds queued at once only runs the last.