CompatHelper: bump compat for BlockBandedMatrices to 0.12 for package ApproxFunBaseTest, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the BlockBandedMatrices package from 0.10, 0.11 to 0.10, 0.11, 0.12 for package ApproxFunBaseTest.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov]

Codecov Report

Patch coverage: 92.85% and project coverage change: -0.05 ⚠️

Comparison is base (a1225ba) 71.90% compared to head (b8ce1b0) 71.85%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #422      +/-   ##
==========================================
- Coverage   71.90%   71.85%   -0.05%     
==========================================
  Files          80       80              
  Lines        8479     8489      +10     
==========================================
+ Hits         6097     6100       +3     
- Misses       2382     2389       +7     

Impacted Files	Coverage Δ
src/Operators/banded/ConstantOperator.jl	78.31% <90.90%> (+1.28%)	⬆️
src/Caching/banded.jl	68.80% <100.00%> (ø)
src/Caching/ragged.jl	63.68% <100.00%> (ø)
src/Space.jl	85.23% <100.00%> (-0.37%)	⬇️

... and 4 files with indirect coverage changes

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