fix allocations of P4estMesh2D BCs

[ranocha]

Closes #1635

[github-actions]

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[DanielDoehring]

Maybe it makes sense to adapt the 3D case

Trixi.jl/src/solvers/dgsem_p4est/dg_3d.jl

Lines 357 to 359 in 27d4fd1

	function calc_boundary_flux!(cache, t, boundary_condition, boundary_indexing,
	mesh::P4estMesh{3},
	equations, surface_integral, dg::DG)

also correspondingly (also allocations are not yet observed)

function calc_boundary_flux!(cache, t, boundary_condition::BC, boundary_indexing,
                             mesh::P4estMesh{3},
                             equations, surface_integral, dg::DG) where {BC}

Similarly, one could also add this to

Trixi.jl/src/solvers/dgmulti/dg_parabolic.jl

Lines 211 to 212 in 27d4fd1

	function calc_boundary_flux!(flux, u, t, operator_type, boundary_conditions,
	mesh, equations, dg::DGMulti, cache, cache_parabolic)

Trixi.jl/src/solvers/dgmulti/dg.jl

Lines 463 to 464 in 27d4fd1

	function calc_boundary_flux!(cache, t, boundary_conditions, mesh,
	have_nonconservative_terms, equations, dg::DGMulti)

Trixi.jl/src/solvers/dgsem_unstructured/dg_2d.jl

Lines 316 to 318 in 27d4fd1

	function calc_boundary_flux!(cache, t, boundary_conditions,
	mesh::Union{UnstructuredMesh2D, P4estMesh, T8codeMesh},
	equations, surface_integral, dg::DG)

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -2.14% ⚠️

Comparison is base (27d4fd1) 92.94% compared to head (b3f4349) 90.80%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1636      +/-   ##
==========================================
- Coverage   92.94%   90.80%   -2.14%     
==========================================
  Files         416      416              
  Lines       34065    34100      +35     
==========================================
- Hits        31661    30963     -698     
- Misses       2404     3137     +733     

Flag	Coverage Δ
unittests	90.80% <100.00%> (-2.14%)	⬇️

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Files Changed	Coverage Δ
src/solvers/dgsem_p4est/dg_2d.jl	97.51% <100.00%> (ø)

... and 72 files with indirect coverage changes

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[ranocha]

Thanks for your quick review! I checked the places you mentioned before submitting this PR. They do not need any treatment since they don't trigger Julia's heuristic to avoid specialization.