[jnigen][infra] Flaky NoClassDefFoundError

I believe I have seen this error flaky on the CI before.

I'll hit rerun on the CI to see if it turns green, but we should try to squash the flakiness!

```
❌ test\generated_runtime_test.dart: kotlin_test_c_based Suspend functions (failed)
Exception in Java code called through JNI: java.lang.NoClassDefFoundError: com/github/dart_lang/jnigen/SuspendFun

java.lang.NoClassDefFoundError: com/github/dart_lang/jnigen/SuspendFun
Caused by: java.lang.ClassNotFoundException: com.github.dart_lang.jnigen.SuspendFun
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:581)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:527)


package:jni/src/accessors.dart 116:5 JniAccessorWrappers.throwException
package:jni/src/accessors.dart 16:19 _check
package:jni/src/accessors.dart 21:19 JniResultMethods.check
package:jni/src/accessors.dart 59:5 JniResultMethods.object
test\kotlin_test\c_based\dart_bindings\kotlin.dart 52:39 new SuspendFun
test\kotlin_test\runtime_test_registrant.dart 16:28 registerTests...
package:ffi/src/arena.dart 124:31 using
test\kotlin_test\runtime_test_registrant.dart 15:13 registerTests..
✅ test\generated_runtime_test.dart: jackson_core_test_c_based simple json parsing test
✅ test\generated_runtime_test.dart: jackson_core_test_c_based parsing invalid JSON throws JniException
❌ test\generated_runtime_test.dart: kotlin_test_dart_only Suspend functions (failed)
Exception in Java code called through JNI: java.lang.NoClassDefFoundError: com/github/dart_lang/jnigen/SuspendFun

java.lang.NoClassDefFoundError: com/github/dart_lang/jnigen/SuspendFun
Caused by: java.lang.ClassNotFoundException: com.github.dart_lang.jnigen.SuspendFun
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:581)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:527)


package:jni/src/accessors.dart [116](https://github.com/dart-lang/native/actions/runs/7035876071/job/19147336010?pr=837#step:12:117):5 JniAccessorWrappers.throwException
package:jni/src/accessors.dart 16:19 _check
package:jni/src/accessors.dart 92:5 JniClassLookupResultMethods.checkedClassRef
package:jni/src/jni.dart 215:20 Jni.findClass.
package:ffi/src/arena.dart [124](https://github.com/dart-lang/native/actions/runs/7035876071/job/19147336010?pr=837#step:12:126):31 using
package:jni/src/jni.dart 213:55 Jni.findClass
package:jni/src/jni.dart 221:22 Jni.findJClass
test\kotlin_test\dart_only\dart_bindings\kotlin.dart 39:15 SuspendFun._class
test\kotlin_test\dart_only\dart_bindings\kotlin.dart SuspendFun._class
test\kotlin_test\dart_only\dart_bindings\kotlin.dart 50:28 new SuspendFun
test\kotlin_test\runtime_test_registrant_dartonly_generated.dart 18:28 registerTests...
package:ffi/src/arena.dart 124:31 using
test\kotlin_test\runtime_test_registrant_dartonly_generated.dart 17:13 registerTests..
```

https://github.com/dart-lang/native/actions/runs/7035876071/job/19147336010?pr=837