Fix MISRA C++ 2023 rule 12.3.1 "The union keyword shall not be used"

[mohammedRafeeque]

Zserio version and language
Zserio: latest from master
Commit date: 6 days ago (6/4/2024 7:12:28 PM)
Commit hash: b8cc6c0

Describe the bug
1 Misra warning getting reported

1. union UntypedHolder

<style> </style>

SNo	Rule	Severity	Message	Filename	Linenumber
1677	MISRACPP2023-12_3_1-a	2	The 'union' keyword shall not be used	/zserio_runtime/include/roadgraph_reliable/zserio_runtime/zserio/AnyHolder.h	296

Please check possibility of fixing the same.

Steps to reproduce the behavior:
SCA run using MISRA 2023 configuration.

Expected behavior
No SCA warnings for MISRA 2023 ruleset

Additional context
N.A

@Roland-Homeier @mikir FYI.

[Mi-La]

The sonar rule M23_158 is already enabled and we have a single accepted issue as an exception:

Module	Line	Command	Link
AnyHolder.h	296	union UntypedHolder	SonarCloud