minecraft-server: move to the java25 line (4.1.0+up2026.8.2.java25)

Minecraft 26.2 requires Java 25, so the chart's default minecraft.version can
only be raised on a java25 image. appVersion becomes 2026.8.2-java25 - the same
dated upstream release the java21 line ships, so the only variables that change
are the JVM and the Minecraft version.

The chart version stays at 4.1.0: the Java lines are siblings of one chart
generation, not successors, and are told apart by the +up suffix.

The Java boundaries in the values.yaml / NOTES.txt comments are read off
Mojang's version manifest (javaVersion.majorVersion per release), not
estimated: 1.21.11 is the last release asking for Java 21, every release from
26.1 on asks for Java 25.

ci/minecraft-server/test-values.yaml

@@ -4,10 +4,10 @@
 # minecraft.version is deliberately NOT set here any more. Since chart 1.0.0 the
 # chart ships a pinned default that belongs to the Java line it publishes (the
 # image tag comes from .Chart.AppVersion, and Java 8 runs Minecraft only up to
-# 1.16.5, 1.18-1.20.4 need Java 17, 1.20.5+ need Java 21). Leaving it unset
-# means the install-test exercises exactly the default a user would get, so a
-# Java line published with a mismatched default version fails CI instead of
-# passing on a CI-only override.
+# 1.16.5, 1.18-1.20.4 need Java 17, 1.20.5-1.21.11 need Java 21 and 26.1+ needs
+# Java 25). Leaving it unset means the install-test exercises exactly the
+# default a user would get, so a Java line published with a mismatched default
+# version fails CI instead of passing on a CI-only override.
 #
 # server.service.type is not set either: the default is ClusterIP, which is what
 # all three real deployments run (routing is done by the static mappings of the