Bump BenchmarkDotNet from 0.13.1 to 0.15.4

---
updated-dependencies:
- dependency-name: BenchmarkDotNet
  dependency-version: 0.15.4
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

Ix.NET/Source/Benchmarks.System.Interactive/Benchmarks.System.Interactive.csproj

@@ -20,7 +20,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.13.1" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.15.4" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(Configuration)|$(Platform)'=='Ix.net 3.1.1|AnyCPU'">