Preserve pinned Java toolchains in release dispatcher

[SkyBlade1978]

Summary

• keep an exact pinned target JDK as the Gradle runtime when its Java major already satisfies the branch metadata
• install a separate Gradle JDK only when the target toolchain major differs
• retain the existing Java 8/16 toolchain plus Java 17 Gradle path for OreSpawn 1.10.2 through 1.17.1
• apply the same selection to both the immutable build and Maven publication jobs
• add dispatcher contracts covering Java 8, 16, pinned/generic 17, and future Java 21 cases

Why

The OreSpawn 1.18.2 release run installed the required Temurin 17.0.1+12 toolchain, then the generic Gradle Java 17 setup replaced it with the runner's Temurin 17.0.20+1. The branch's final toolchain audit correctly rejected that replacement. Normal branch CI was green because it uses only the pinned installation.

Failed run: https://github.com/MinecraftModDevelopmentMods/OreSpawn/actions/runs/33113841570/job/98663359941

Validation

• actionlint 1.7.12 passes for deploy-release.yml
• git diff --check passes
• the current MMD metadata matrix passes for every enabled target from 1.10.2 through 1.18.2
• Java 8/16 targets still select a separate Java 17 Gradle runtime
• pinned Temurin 17.0.1+12 on 1.18.2 remains the active Gradle runtime
• malformed toolchain versions are rejected

The failed release created no tag and published nothing to Maven, CurseForge, or GitHub, so 4.0.10.118021 can be retried after this dispatcher change is merged.