Fix some typos in XML docs

[martintmk]

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 #1458 (2396832) into main (0047a84) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1458   +/-   ##
=======================================
  Coverage   83.92%   83.92%           
=======================================
  Files         274      274           
  Lines        6506     6506           
  Branches     1012     1012           
=======================================
  Hits         5460     5460           
  Misses        837      837           
  Partials      209      209           

Flag	Coverage Δ
linux	83.92% <ø> (ø)
macos	83.92% <ø> (ø)
windows	83.92% <ø> (ø)

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Files Changed	Coverage Δ
src/Polly.Core/ResilienceStrategy.cs	100.00% <ø> (ø)
src/Polly.Core/ResilienceStrategyT.Async.cs	100.00% <ø> (ø)