fix: src/LittleBlocks.Notifications.Messaging.MailKit/LittleBlocks.Notifications.Messaging.MailKit.csproj to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-DOTNET-SYSTEMFORMATSASN1-7443633

Author: snyk-bot

src/LittleBlocks.Notifications.Messaging.MailKit/LittleBlocks.Notifications.Messaging.MailKit.csproj

@@ -14,7 +14,7 @@
     </PropertyGroup>
 
     <ItemGroup>
-        <PackageReference Include="MailKit" Version="3.4.3" />
+        <PackageReference Include="MailKit" Version="4.9.0" />
         <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="6.0.3" />
         <PackageReference Include="Microsoft.Extensions.Options" Version="6.0.0" />
     </ItemGroup>