Update dependency java to v21 (#1391)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [java](https://adoptium.net) | major | `17.0.15+6` -> `21.0.7+6.0.LTS`
|

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mise.toml

@@ -2,7 +2,7 @@
 "cargo:zizmor" = "1.8.0"
 "go:github.com/gohugoio/hugo" = "v0.147.0"
 "go:github.com/grafana/oats" = "0.3.1"
-java = "temurin-17.0.15+6"
+java = "temurin-21.0.7+6.0.LTS"
 lychee = "0.18.1"
 protoc = "31.0"