upgrade to NET7 and C# 11

[rkm]

Proposed Changes

Upgrades the SDK and language versions.

Types of changes

What types of changes does your code introduce? Tick all that apply.

• Bugfix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that would cause existing functionality to not work as expected)
• Documentation-Only Update (if none of the other choices apply)
  • In this case, ensure that the message of the head commit from the source branch is prefixed with [skip ci]

Checklist

By opening this PR, I confirm that I have:

• Reviewed the contributing guidelines for this repository
• Ensured that the PR branch is in sync with the target branch (i.e. it is automatically merge-able)
• Updated any relevant API documentation
• Created or updated any tests if relevant
• Created a news file
  • NOTE: This must include any changes to any of the following files: default.yaml, any of the RabbitMQ server configurations, GlobalOptions.cs
• Listed myself in the CONTRIBUTORS file 🚀
• Requested a review by one of the repository maintainers

Issues

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (7e85918) 68.50% compared to head (45a79f3) 68.50%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1637   +/-   ##
=======================================
  Coverage   68.50%   68.50%           
=======================================
  Files         185      185           
  Lines        6550     6550           
=======================================
  Hits         4487     4487           
  Misses       2063     2063           

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