IONOS(build): reduce code duplication and improve error handling in workflow

[Copilot]

Summary

Addresses code review feedback to eliminate repeated expressions, improve error handling, and enhance code maintainability in the build workflow.

Cache Version Computation:

• Centralized repeated cache version expression (CACHE_VERSION + optional suffix) into a single computed output in prepare-matrix job
• Eliminated duplication across 4 locations (lines 195, 307, 340, 1201) by referencing effective_cache_version output

Error Handling:

• Added trap cleanup EXIT in get-job-data action to guarantee temporary file cleanup in all exit paths (success, error, early exit)

Code Quality:

• Replaced xargs-based whitespace trimming with bash parameter expansion for better readability
• Added explanatory comments for IFS array joining technique used in property string construction

TODO

• ...

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

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