Bump the testing group with 3 updates

Bumps FluentAssertions from 8.6.0 to 8.8.0
Bumps Microsoft.NET.Test.Sdk from 17.14.1 to 18.0.0
Bumps xunit.runner.visualstudio from 3.1.4 to 3.1.5

---
updated-dependencies:
- dependency-name: FluentAssertions
  dependency-version: 8.8.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: testing
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: testing
- dependency-name: xunit.runner.visualstudio
  dependency-version: 3.1.5
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: testing
...

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

Author: dependabot[bot]

BaldersGait.UnitTests/BaldersGait.UnitTests.csproj

@@ -12,10 +12,10 @@
     </PropertyGroup>
 
     <ItemGroup>
-        <PackageReference Include="FluentAssertions" Version="8.6.0" />
-        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1"/>
+        <PackageReference Include="FluentAssertions" Version="8.8.0" />
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.0.0"/>
         <PackageReference Include="xunit" Version="2.9.3"/>
-        <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4">
+        <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
             <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
             <PrivateAssets>all</PrivateAssets>
         </PackageReference>