Update minecraft-server to the java17 line (3.0.0+up2026.8.2.java17)

Second of the three publishes that carry the checksum annotations from
3.0.0+up2026.8.2.java8. Same chart content, only the published Java line
changes: appVersion moves to the dated tag 2026.8.2-java17 and the
minecraft.version default moves to 1.20.1, the line's matching Minecraft
version (Java 8 runs up to 1.16.5, 1.18-1.20.4 need Java 17, 1.20.5+ need
Java 21).

Refs #82.

minecraft-server/Chart.yaml

@@ -13,8 +13,8 @@ type: application
 # continuously, so a pod restart could pull a different image than the last one
 # without anything being recorded anywhere. The dated tags are immutable, so the
 # image is now pinned by the chart version like every other chart in this repo.
-version: 3.0.0+up2026.8.2.java8
-appVersion: "2026.8.2-java8"
+version: 3.0.0+up2026.8.2.java17
+appVersion: "2026.8.2-java17"
 
 maintainers:
   - name: jklein