Bump MQTTnet from 3.0.14 to 3.0.15

Created by: dependabot-preview[bot]

Bumps MQTTnet from 3.0.14 to 3.0.15.

Release notes

Sourced from MQTTnet's releases.

v3.0.15

• [Core] Fixed some issues in nuget packages.
• [Client] Changed exception types so that proper exceptions are thrown when connecting (#1082).
• [Client] Exposed Dup flag in application messages.
• [Client] Improved keep alive message sending.
• [RpcClient] Fixed an issue when using a custom application message reveived handler (#1093).
• [RpcClient] Fixed a race condition when using timeout and cancellation token at the same time (BREAKING CHANGE!).
• [Server] Improved keep alive message sending.

Commits

• 12f3461 Improve RPC client handling.
• 0582734 Update codeql-analysis.yml
• 1e88d6a Merge remote-tracking branch 'origin/master'
• 8261ba9 Update docs.
• b766c1b Refactor keep alive message handling in order to fix issues with sudden disco...
• 6c18889 Create codeql-analysis.yml
• 2d4ea8e Improve nuget packages.
• 15d3761 Merge pull request #1097 from yyjdelete/nuspec
• ed52045 Use the data converter only when creating packets.
• cfc4ebe Expose Dup flag in application messages (#1096).
• Additional commits viewable in compare view

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