[7.0] CI build fails unless `syncMavenizer` is run before `build`

[Choonster]

• ForgeGradle version: 7.0.0-beta.51
• Minecraft version: 1.21.11
• Forge version: 61.0.1

When running the build task in a CI build (e.g. GitHub Actions), it will fail with compilation errors unless syncMavenizer is manually run beforehand. In ForgeGradle 6, running build was enough to trigger the workspace setup.

This doesn't happen when opening the project in IntelliJ IDEA, which automatically runs syncMavenizer.

• Minimal reproduction: https://github.com/Choonster-Minecraft-Mods/ForgeGradle7CITestMod
• Failed run with only build: https://github.com/Choonster-Minecraft-Mods/ForgeGradle7CITestMod/actions/runs/20110334595/job/57705630921
• Successful run with syncMavenizer: https://github.com/Choonster-Minecraft-Mods/ForgeGradle7CITestMod/actions/runs/20110678909/job/57706817950