Fix serialization flag handling in ReflectiveClassBuildItem.MultiBuildItem

[famod]

Stumbled upon this while reviewing quarkiverse/quarkus-cxf#347 because Eclipse showed a warning.

Broken since the very beginning, AFAICS: #15380

[quarkus-bot]

This workflow status is outdated as a new workflow run has been triggered.

Failing Jobs - Building 89b3807

Status	Name	Step	Failures	Logs	Raw logs
✖	Initial JDK 11 Build	Build	Failures	Logs	Raw logs

Failures

⚙️ Initial JDK 11 Build #

- Failing: core/deployment 
! Skipped: core/test-extension/deployment core/test-extension/runtime devtools/bom-descriptor-json and 619 more

📦 core/deployment

✖ Failed to execute goal net.revelc.code.formatter:formatter-maven-plugin:2.17.1:validate (default) on project quarkus-core-deployment: File '/home/runner/work/quarkus/quarkus/core/deployment/src/main/java/io/quarkus/deployment/builditem/nativeimage/ReflectiveClassBuildItem.java' has not been previously formatted. Please format file and commit before running validation!

[famod]

The fact that this has gone unnoticed for so long makes me wonder whether it's used at all.

[gastaldi]

The fact that this has gone unnoticed for so long makes me wonder whether it's used at all.

+1, perhaps we can remove it but better check with the author first

[geoand]

Good catch!

[gsmet]

Three of you around and and it didn't even have a backport label?!? :)