fix(backport): Guard Minuit optimizer against provided strategy of None

[matthewfeickert]

Description

• Backport:
  • PR fix: Correct handling of strategy 0 for Minuit optimizer #2277
  • PR fix: Guard Minuit optimizer against provided strategy of None #2278

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

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For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Backport:
   - PR https://github.com/scikit-hep/pyhf/pull/2277
   - PR https://github.com/scikit-hep/pyhf/pull/2278

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release/v0.7.x@616966d). Click here to learn what that means.
Patch has no changes to coverable lines.

Additional details and impacted files

@@                Coverage Diff                @@
##             release/v0.7.x    #2288   +/-   ##
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  Coverage                  ?   98.23%           
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  Files                     ?       69           
  Lines                     ?     4540           
  Branches                  ?      802           
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  Hits                      ?     4460           
  Misses                    ?       47           
  Partials                  ?       33           

Flag	Coverage Δ
contrib	27.53% <0.00%> (?)
doctest	61.03% <0.00%> (?)
unittests-3.10	96.27% <0.00%> (?)
unittests-3.11	96.27% <0.00%> (?)
unittests-3.7	96.25% <0.00%> (?)
unittests-3.8	96.29% <0.00%> (?)
unittests-3.9	96.32% <0.00%> (?)

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