Make more tests compatible with 1.11

[gdalle]

DI source

• Ensure that hvp_mode never returns nothing

DIT source

• Improve compatibility tests for scenarios to exclude those that will never work with AutoSparse, SecondOrder or a combination thereof

DI tests

• Replace Enzyme with ReverseDiff in SparsityDetector tests
• Put SecondOrder(AutoForwardDiff, X) tests inside X tests, for X in [AutoZygote, AutoReverseDiff] (no new deps)
• Put SecondOrder(AutoEnzyme, AutoEnzyme) tests inside Enzyme tests
• Shorten sparse backend construction with MyAutoSparse

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.39%. Comparing base (a074f88) to head (ef416fd).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #552      +/-   ##
==========================================
+ Coverage   98.29%   98.39%   +0.10%     
==========================================
  Files         108      107       -1     
  Lines        4742     4739       -3     
==========================================
+ Hits         4661     4663       +2     
+ Misses         81       76       -5     

Flag	Coverage Δ
DI	98.63% <100.00%> (+0.15%)	⬆️
DIT	97.90% <100.00%> (+<0.01%)	⬆️

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