Bump BenchmarkDotNet from 0.15.4 to 0.15.6

---
updated-dependencies:
- dependency-name: BenchmarkDotNet
  dependency-version: 0.15.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

tools/ProgressOnderwijsUtilsBenchmarks/ProgressOnderwijsUtilsBenchmarks.csproj

@@ -6,7 +6,7 @@
     <TieredCompilation>false</TieredCompilation>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.15.4" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.15.6" />
     <PackageReference Include="Dapper" Version="2.1.66" />
     <PackageReference Include="IncrementalMeanVarianceAccumulator" Version="1.0.0" />
     <PackageReference Include="JetBrains.Annotations" Version="2025.2.2" />