Fix maven BuildIT failures

The dependency `stax-api` is not compatible with the dependency `quarkus-jaxb` because both add the same type `javax.xml.namespace.QName`. This was done on purpose to validate the `parent-first-artifacts` property when building projects with conflicts with Maven, so we need to skip the JaxbContext validation at build time.

This pull request should fix all the CI failures in the latest pull requests.

extensions/jaxb/deployment/src/main/java/io/quarkus/jaxb/deployment/JaxbProcessor.java

@@ -313,8 +313,11 @@ void setupJaxbContextConfig(JaxbConfig config,
 
         // parse class names to class
         Set<Class<?>> classes = getAllClassesFromClassNames(classNamesToBeBound);
-        // validate the context to fail at build time if it's not valid
-        validateContext(classes);
+        if (config.validateJaxbContext) {
+            // validate the context to fail at build time if it's not valid
+            validateContext(classes);
+        }
+
         // register the classes to be used at runtime
         jaxbContextConfig.addClassesToBeBound(classes);
     }

extensions/jaxb/runtime/src/main/java/io/quarkus/jaxb/runtime/JaxbConfig.java

@@ -9,6 +9,13 @@
 
 @ConfigRoot(phase = ConfigPhase.BUILD_AND_RUN_TIME_FIXED, name = "jaxb")
 public class JaxbConfig {
+
+    /**
+     * If enabled, it will validate the default JAXB context at build time.
+     */
+    @ConfigItem(defaultValue = "true")
+    public boolean validateJaxbContext;
+
     /**
      * Exclude classes to automatically be bound to the default JAXB context.
      */

integration-tests/maven/src/test/resources-filtered/projects/classloader-linkage-error/src/main/resources/application.properties

@@ -1 +1,5 @@
 quarkus.class-loading.parent-first-artifacts=stax:stax-api
+# The dependency `stax-api` is not compatible with the dependency `quarkus-jaxb` because both add the same
+# type `javax.xml.namespace.QName`. This was done on purpose to validate the `parent-first-artifacts` property when building
+# projects with conflicts with Maven, so we need to skip the JaxbContext validation at build time.
+quarkus.jaxb.validate-jaxb-context=false