Bump MailKit from 4.14.1 to 4.15.0

---
updated-dependencies:
- dependency-name: MailKit
  dependency-version: 4.15.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

Refresh.Core/Refresh.Core.csproj

@@ -22,7 +22,7 @@
         <PackageReference Include="CommandLineParser" Version="2.9.1" />
         <PackageReference Include="Discord.Net.Webhook" Version="3.18.0" />
         <PackageReference Include="DnsClient" Version="1.8.0" />
-        <PackageReference Include="MailKit" Version="4.14.1" />
+        <PackageReference Include="MailKit" Version="4.15.0" />
         <PackageReference Include="NPTicket" Version="3.1.1" />
         <PackageReference Include="Pfim" Version="0.11.3" />
         <PackageReference Include="SharpZipLib" Version="1.4.2" />