Adjust to !(AbstractQ <: AbstractMatrix)

[dkarrasch]

This makes the package future proof for JuliaLang/julia#46196. Some of the tests look complicated which is due to the fact that Matrix(Q) doesn't work.

[codecov]

Codecov Report

Base: 77.31% // Head: 78.10% // Increases project coverage by +0.78% 🎉

Coverage data is based on head (901c247) compared to base (90002ca).
Patch coverage: 70.58% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #122      +/-   ##
==========================================
+ Coverage   77.31%   78.10%   +0.78%     
==========================================
  Files          11       11              
  Lines        1305     1306       +1     
==========================================
+ Hits         1009     1020      +11     
+ Misses        296      286      -10     

Impacted Files	Coverage Δ
src/blockbanded/blockbanded.jl	94.87% <ø> (ø)
src/infql.jl	46.51% <42.85%> (ø)
src/InfiniteLinearAlgebra.jl	90.90% <50.00%> (+2.67%)	⬆️
src/banded/hessenbergq.jl	71.84% <66.66%> (+9.70%)	⬆️
src/banded/infbanded.jl	81.60% <66.66%> (ø)
src/banded/infqltoeplitz.jl	69.16% <85.71%> (-0.59%)	⬇️
src/infqr.jl	97.55% <100.00%> (+0.01%)	⬆️

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[dkarrasch]

Gentle bump.