Repository: quarkusio/quarkus
Issue: Quarkus 2.13 test extension tests fail with the 22.3 mandrel builder image

### Describe the bug

The integration tests fail with the 22.3 mandrel builder image. Filing this for tracking purposes:

```
[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running io.quarkus.it.extension.ClasspathInGraalITCase
Executing "/home/runner/work/mandrel/mandrel/quarkus/integration-tests/test-extension/tests/target/quarkus-integration-test-test-extension-tests-999-SNAPSHOT-runner -Dquarkus.http.port=8081 -Dquarkus.http.ssl-port=8444 -Dtest.url=http://localhost:8081 -Dquarkus.log.file.path=/home/runner/work/mandrel/mandrel/quarkus/integration-tests/test-extension/tests/target/quarkus.log -Dquarkus.log.file.enable=true"
Mar 25, 2023 2:19:24 AM io.quarkus.runtime.ApplicationLifecycleManager run
ERROR: Failed to start application (with profile prod)
java.lang.ClassNotFoundException: io.quarkus.extest.runtime.config.RunTimeConfigBuilder
	at java.base@17.0.6/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:52)
	at java.base@17.0.6/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
	at java.base@17.0.6/java.lang.ClassLoader.loadClass(ClassLoader.java:132)
	at io.quarkus.runtime.configuration.ConfigUtils.configBuilder(ConfigUtils.java:189)
	at io.quarkus.runtime.generated.Config.readConfig(Unknown Source)
	at io.quarkus.deployment.steps.RuntimeConfigSetup.deploy(Unknown Source)
	at io.quarkus.runner.ApplicationImpl.doStart(Unknown Source)
	at io.quarkus.runtime.Application.start(Application.java:101)
	at io.quarkus.runtime.ApplicationLifecycleManager.run(ApplicationLifecycleManager.java:110)
	at io.quarkus.runtime.Quarkus.run(Quarkus.java:70)
	at io.quarkus.runtime.Quarkus.run(Quarkus.java:43)
	at io.quarkus.runtime.Quarkus.run(Quarkus.java:123)
	at io.quarkus.runner.GeneratedMain.main(Unknown Source)
```

### Expected behavior

Test extension tests pass with the builder image.

### Actual behavior

Test throws `ClassNotFoundException` at boot.

### How to Reproduce?

Run integration tests extension tests with the 22.3 builder image.

### Output of `uname -a` or `ver`

_No response_

### Output of `java -version`

_No response_

### GraalVM version (if different from Java)

_No response_

### Quarkus version or git rev

_No response_

### Build tool (ie. output of `mvnw --version` or `gradlew --version`)

_No response_

### Additional information

See https://github.com/graalvm/mandrel/actions/runs/4516801805/jobs/7955690955#step:11:1120

Changed files:
core/deployment/src/main/java/io/quarkus/deployment/steps/ConfigGenerationBuildStep.java

diff --git a/core/deployment/src/main/java/io/quarkus/deployment/steps/ConfigGenerationBuildStep.java b/core/deployment/src/main/java/io/quarkus/deployment/steps/ConfigGenerationBuildStep.java
index 33453e60485..3d48d5f38f6 100644
--- a/core/deployment/src/main/java/io/quarkus/deployment/steps/ConfigGenerationBuildStep.java
+++ b/core/deployment/src/main/java/io/quarkus/deployment/steps/ConfigGenerationBuildStep.java
@@ -265,6 +265,11 @@ void generateConfigClass(
         runtimeMappings.addAll(configItem.getReadResult().getBuildTimeRunTimeMappings());
         runtimeMappings.addAll(configItem.getReadResult().getRunTimeMappings());
 
+        Set<String> runtimeConfigBuilderClassNames = runTimeConfigBuilders.stream()
+                .map(RunTimeConfigBuilderBuildItem::getBuilderClassName).collect(toSet());
+        reflectiveClass
+                .produce(new ReflectiveClassBuildItem(false, false, runtimeConfigBuilderClassNames.toArray(new String[0])));
+
         RunTimeConfigurationGenerator.GenerateOperation
                 .builder()
                 .setBuildTimeReadResult(configItem.getReadResult())
@@ -285,8 +290,7 @@ void generateConfigClass(
                 .setRuntimeConfigSourceProviders(discoveredConfigSourceProviders)
                 .setRuntimeConfigSourceFactories(discoveredConfigSourceFactories)
                 .setRuntimeConfigMappings(runtimeMappings)
-                .setRuntimeConfigBuilders(
-                        runTimeConfigBuilders.stream().map(RunTimeConfigBuilderBuildItem::getBuilderClassName).collect(toSet()))
+                .setRuntimeConfigBuilders(runtimeConfigBuilderClassNames)
                 .build()
                 .run();
     }