Add adjoint ops to device test suite

[albi3ro]

While #2222 added default.qubit support for several non-decomposable Adjoint gates, they were not added to the device test suite. This PR adds the following ops to the device test suite:

• adjoint(S)
• adjoint(T)
• adjoint(SX)
• adjoint(SISWAP)
• adjoint(ISWAP)

[codecov]

Codecov Report

Merging #2658 (c5e8d3a) into master (43fc4f6) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           master    #2658    +/-   ##
========================================
  Coverage   99.58%   99.58%            
========================================
  Files         248      249     +1     
  Lines       19985    20135   +150     
========================================
+ Hits        19902    20052   +150     
  Misses         83       83            

Impacted Files	Coverage Δ
pennylane/math/single_dispatch.py	98.86% <ø> (ø)
pennylane/ops/op_math/__init__.py	100.00% <100.00%> (ø)
pennylane/ops/op_math/pow_class.py	100.00% <100.00%> (ø)

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[rmoyard]

Thank you for adding the adjoint operations to the tests 💯 It looks good to me!