Minor API cleanup

[martintmk]

Details on the issue fix or feature implementation

Contributes to #1507

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[codecov]

Codecov Report

Merging #1508 (71db9fe) into main (a61b343) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1508   +/-   ##
=======================================
  Coverage   83.86%   83.86%           
=======================================
  Files         272      272           
  Lines        6481     6481           
  Branches     1020     1020           
=======================================
  Hits         5435     5435           
  Misses        837      837           
  Partials      209      209           

Flag	Coverage Δ
linux	?
macos	83.86% <100.00%> (ø)
windows	83.86% <100.00%> (ø)

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Files Changed	Coverage Δ
src/Polly.Core/Retry/OnRetryArguments.cs	100.00% <100.00%> (ø)
src/Polly.Testing/ResiliencePipelineDescriptor.cs	100.00% <100.00%> (ø)
src/Polly.Testing/ResilienceStrategyDescriptor.cs	100.00% <100.00%> (ø)