Correct drupal-check issue

Problem/Motivation

After running the latest version of drupal-check on the module, it flagged the following issue:

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  Line   layout_builder_additions/src/LayoutBuilderBlockFormTitle.php                                                                                      
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  85     Method Drupal\layout_builder_additions\LayoutBuilderBlockFormTitle::getLabelFromPluginId() should return string but return statement is missing.  
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Steps to reproduce

• Run drupal-check against the module.

Proposed resolution

• Fix the issue. A string should be returned no matter what.

Remaining tasks

Complete the work.

User interface changes

N/A

API changes

N/A

Data model changes

N/A