MINOR: [C#] Bump coverlet.collector to 6.0.4

---
updated-dependencies:
- dependency-name: coverlet.collector
  dependency-version: 6.0.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: coverlet.collector
  dependency-version: 6.0.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

csharp/test/Apache.Arrow.Flight.Sql.Tests/Apache.Arrow.Flight.Sql.Tests.csproj

@@ -9,7 +9,7 @@
       <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
       <PackageReference Include="xunit" Version="2.9.2" />
       <PackageReference Include="xunit.runner.visualstudio" Version="3.0.0" />
-      <PackageReference Include="coverlet.collector" Version="6.0.3" />
+      <PackageReference Include="coverlet.collector" Version="6.0.4" />
     </ItemGroup>
 
     <ItemGroup>

csharp/test/Apache.Arrow.Flight.Tests/Apache.Arrow.Flight.Tests.csproj

@@ -9,7 +9,7 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="xunit" Version="2.9.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.0.0" />
-    <PackageReference Include="coverlet.collector" Version="6.0.3" />
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
   </ItemGroup>
 
   <ItemGroup>