Fix config converter loading issue when arrays are used

We essentially use Class.forName to load the class instead of the
ClassLoader directly, as the former knows how to deal with arrays

Fixes: quarkusio#46170

core/runtime/src/main/java/io/quarkus/runtime/configuration/AbstractConfigBuilder.java

@@ -25,7 +25,7 @@ protected static void withDefaultValue(SmallRyeConfigBuilder builder, String nam
     protected static <T> void withConverter(SmallRyeConfigBuilder builder, String type, int priority, Converter<T> converter) {
         try {
             // To support converters that are not public
-            builder.withConverter((Class<T>) builder.getClassLoader().loadClass(type), priority, converter);
+            builder.withConverter((Class<T>) Class.forName(type, false, builder.getClassLoader()), priority, converter);
         } catch (ClassNotFoundException e) {
             throw new RuntimeException(e);
         }

integration-tests/test-extension/extension/deployment/src/test/java/io/quarkus/config/ByteArrayConverterTest.java

@@ -0,0 +1,28 @@
+package io.quarkus.config;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.nio.charset.StandardCharsets;
+
+import org.eclipse.microprofile.config.inject.ConfigProperty;
+import org.jboss.shrinkwrap.api.ShrinkWrap;
+import org.jboss.shrinkwrap.api.spec.JavaArchive;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.quarkus.test.QuarkusUnitTest;
+
+public class ByteArrayConverterTest {
+    @RegisterExtension
+    static final QuarkusUnitTest TEST = new QuarkusUnitTest()
+            .setArchiveProducer(() -> ShrinkWrap.create(JavaArchive.class))
+            .overrideConfigKey("someapp.bytearray", "XyZ*123");
+
+    @ConfigProperty(name = "someapp.bytearray")
+    protected byte[] bytearray;
+
+    @Test
+    void buildTimeConfigBuilder() {
+        assertEquals("XyZ*123", new String(bytearray, StandardCharsets.UTF_8));
+    }
+}

integration-tests/test-extension/extension/runtime/src/main/java/io/quarkus/extest/runtime/config/ByteArrayConfigConverter.java

@@ -0,0 +1,13 @@
+package io.quarkus.extest.runtime.config;
+
+import java.nio.charset.StandardCharsets;
+
+import org.eclipse.microprofile.config.spi.Converter;
+
+public class ByteArrayConfigConverter implements Converter<byte[]> {
+
+    @Override
+    public byte[] convert(final String s) {
+        return s.getBytes(StandardCharsets.UTF_8);
+    }
+}

integration-tests/test-extension/extension/runtime/src/main/resources/META-INF/services/org.eclipse.microprofile.config.spi.Converter

@@ -0,0 +1 @@
+io.quarkus.extest.runtime.config.ByteArrayConfigConverter