Adjust lower compats for compatibility with julia-1.11

[fhagemann]

Here are some changes to the lower package compats required to work on julia-1.11:

• The type parameter in AbstractTriangular was removed in julia-1.11.
  As AbstractTriangular was explicitly called in FillArrays until 0.13.8,the compat in the General registry was manually adjusted to disallow the use of FillArrays pre-0.13 with julia-1.11.
  ==> I adjusted the lower compat of FillArrays to 0.13.8.

• BinaryProvider is discontinued in julia-1.11.

  • FFTW directly depended on BinaryProvider until 1.1.
    ==> I adjusted the lower compat of FFTW to 1.2.
  • SpecialFunctions depended on BinaryProvider until 0.8.
    In RadiationDetectorDSP, [email protected] only allows for [email protected].
    ==> I adjusted the lower compat of DSP to 0.6.2 to also allow for [email protected].

These changes should resolve the failing Downgrade tests.
The only question remaining: do we want an explicit version requirement for SpecialFunctions ≥ 0.9 via weak dependencies here?

[oschulz]

These changes should resolve the failing Downgrade tests.

Should we maybe run Downgrade on Julia v1.10 LTS - so kinda downgrade Julia as well?

[fhagemann]

We could. Or is there a possibility to have different Project.toml for each Julia version?

[oschulz]

Or is there a possibility to have different Project.toml for each Julia version

No, that's not possible.

[fhagemann]

I relaxed the package compatibility requirements by setting strict: false in the Downgrade CI.

Final changes:

• I adjusted the lower compat of FillArrays to 0.13.
• I adjusted the lower compat of FFTW to 1.2 to not depend on BinaryProvider.
• Downgrade will now run BOTH on 1.10 and on 1.

@oschulz If all tests pass, this PR should be ready to go.