Remove unchecked warning

[trask]

Noticed this simplification from @zeitlinger when porting this class to use in Spring (open-telemetry/opentelemetry-java-instrumentation#15775).

[codecov]

Codecov Report

❌ Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.21%. Comparing base (c45930b) to head (3406c83).

Files with missing lines	Patch %	Lines
...or/fileconfig/YamlDeclarativeConfigProperties.java	86.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8090   +/-   ##
=========================================
  Coverage     90.21%   90.21%           
- Complexity     7605     7606    +1     
=========================================
  Files           841      841           
  Lines         22923    22924    +1     
  Branches       2291     2291           
=========================================
+ Hits          20681    20682    +1     
  Misses         1525     1525           
  Partials        717      717           

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