Update samples to .NET 8

[martincostello]

• Update various sample projects from net7.0 to net8.0.
• Fix CA1849 warning from updating snippets to .NET 8.
• Fix IDE0034 warning identified by the .NET 9 SDK in Update to .NET 9 SDK #2003.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.64%. Comparing base (3336d1c) to head (8ac8979).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2004   +/-   ##
=======================================
  Coverage   83.64%   83.64%           
=======================================
  Files         312      312           
  Lines        7105     7105           
  Branches     1054     1054           
=======================================
  Hits         5943     5943           
  Misses        789      789           
  Partials      373      373           

Flag	Coverage Δ
linux	?
macos	?
windows	83.64% <ø> (ø)

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