[SSD-4123] Upgrade MediatR to 13.1

[EsgAtWorkleap]

Jira issue link: ssd-4123

Description of changes

Updated MediatR to 13.1
ServiceCollectionExtensions was renamed to MediatRServiceCollectionExtensions

Breaking changes

None, I think

Additional checks

• Updated the documentation of the project to reflect the changes
• Added new tests that cover the code changes
  Was already covered with existing tests

[Copilot]

Pull Request Overview

This PR upgrades MediatR from version 13.0.0 to 13.1.0 and adapts the codebase to accommodate breaking changes introduced in the new version. The primary change involves MediatR renaming its service collection extensions class, requiring updates to the Roslyn analyzer that detects improper usage of the MediatR registration API.

• MediatR package upgraded from 13.0.0 to 13.1.0
• Analyzer updated to reference the renamed MediatRServiceCollectionExtensions class
• Test adjusted to disable service validation due to MediatR 13.1.0 behavior changes

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/Workleap.Extensions.MediatR/Workleap.Extensions.MediatR.csproj	Updates MediatR package reference from 13.0.0 to 13.1.0
src/Workleap.Extensions.MediatR.Tests/HostBuilderTests.cs	Adds ValidateOnBuild=false workaround and required import for MediatR 13.1.0 compatibility
src/Workleap.Extensions.MediatR.Analyzers/ServiceRegistrationAnalyzer.cs	Updates reference to renamed MediatR class and removes BOM character
src/Workleap.Extensions.MediatR.Analyzers/Internals/KnownSymbolNames.cs	Renames constant and updates class name to match MediatR 13.1.0 changes, removes BOM character

Comments suppressed due to low confidence (1)

src/Workleap.Extensions.MediatR.Tests/HostBuilderTests.cs:23

• Corrected grammar: 'is check' should be 'is checked'.

        // The license is check in the constructor of the Mediator.