Fix missing condition variable include

[klecki]

Description

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactoring (Redesign of existing code that doesn't affect functionality)
• Other (e.g. Documentation, Tests, Configuration)

What happened in this PR

Added a missing header to fix compilation on some platforms,
Fixes #3287.

Additional information

• Affected modules and functionalities:

• Key points relevant for the review:

Checklist

Tests

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Documentation

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DALI team only

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JIRA TASK: N/A

[klecki]

!build

[dali-automaton]

CI MESSAGE: [2848819]: BUILD STARTED

[dali-automaton]

CI MESSAGE: [2848819]: BUILD PASSED

[mzient]

I know it's alphabetically sorted, but it seems weird to have sophisticated headers before cstddef... Normally I wouldn't look for cstddef anywhere else than at the very top.