Use SHA256 for ChecksumAlgorithm and fix Binskim warning

[martintmk]

The issue or feature being addressed

Closes #1617

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

Patch and project coverage have no change.

Comparison is base (45b0bde) 84.65% compared to head (8c27f30) 84.65%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1623   +/-   ##
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  Coverage   84.65%   84.65%           
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  Files         306      306           
  Lines        6829     6829           
  Branches     1045     1045           
=======================================
  Hits         5781     5781           
  Misses        839      839           
  Partials      209      209           

Flag	Coverage Δ
linux	?
macos	84.65% <ø> (ø)
windows	84.65% <ø> (ø)

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[martincostello]

LGTM - Would be good to run binskim on the binaries from the build before merging to check it resolves the reported warning.

[martintmk]

LGTM - Would be good to run binskim on the binaries from the build before merging to check it resolves the reported warning.

Looks good:

C:\Development\GitHub\Polly\src\Polly.Core\bin\Debug\net6.0\Polly.Core.dll: pass BA2004: 'Polly.Core.dll' is a managed binary which was compiled with a secure (SHA-256) source code hashing algorithm.