Fix nativeTest failures in CI under GraalVM Native Image

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- See https://github.com/baomidou/dynamic-datasource/actions/runs/20453121808/job/58769886305 .

**Describe the solution you'd like**
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- The native test in CI under the GraalVM Native Image has failed. A further change to a Gradle-style approach is needed.
- The file https://github.com/baomidou/dynamic-datasource/blob/master/CONTRIBUTING.md also needs to be modified.

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- Null.

**Additional context**
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- Given that issues https://github.com/gradle/gradle/issues/17559 and https://github.com/graalvm/native-build-tools/issues/572 remain unresolved, bypassing this problem might seem odd. After all, Gradle's design is outdated compared to Maven. To be honest, I would be very grateful if someone were willing to fix the Gradle bug first.

Start with the failed nativeTest job in the linked GitHub Actions run and inspect the Gradle-style native-image setup. Update CONTRIBUTING.md as requested, then verify that the native test passes in CI and that the documented workflow reflects the change.

Written by the indexing model from the issue text.