Minor perf optimization

[utpilla]

Changes

• Use utf-8 string literal to avoid allocating the string with utf-16 encoding: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/reference-types#utf-8-string-literals

[codecov]

Codecov Report

Merging #5152 (473355f) into main (13791e2) will increase coverage by 0.05%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5152      +/-   ##
==========================================
+ Coverage   83.28%   83.34%   +0.05%     
==========================================
  Files         297      297              
  Lines       12380    12379       -1     
==========================================
+ Hits        10311    10317       +6     
+ Misses       2069     2062       -7     

Flag	Coverage Δ
unittests	83.34% <100.00%> (+0.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...lemetry/Internal/SelfDiagnosticsConfigRefresher.cs	86.53% <100.00%> (ø)

... and 10 files with indirect coverage changes