kdoctor: update to use jdk21

[chenrui333]

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• openjdk: 25.0.1 #250760

[Copilot]

Pull Request Overview

This PR updates the kdoctor formula to use OpenJDK 21 specifically instead of the latest OpenJDK version, and adds the --no-daemon flag to the Gradle build command. It also removes the no_autobump! directive and updates an issue reference URL.

• Pins the OpenJDK dependency to version 21
• Adds --no-daemon flag to Gradle build command
• Updates issue tracker reference from KT-81085 to KMT-1702

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