COMP: Pin libcxx <22 in conda recipe for CastXML 0.7.0 compatibility

CastXML 0.7.0 on conda-forge bundles Clang 20 internally, which
cannot parse the __acquire_capability__ pack-expansion syntax that
libc++ 22 introduced in <mutex>:422.

Without this pin, every wrapped ITK class fails during Python XML
generation with:
  attribute '__acquire_capability__' does not support argument
  pack expansion

Remove this pin when CastXML ships against Clang 22+ (or when
conda-forge tightens castxml-feedstock's own libcxx upper bound).

Author: hjmjohnson

Utilities/conda-packages/recipe.yaml

@@ -36,6 +36,12 @@ outputs:
       - ${{ compiler('c') }}
       - ${{ compiler('cxx') }}
       - castxml >=0.7.0
+      # castxml 0.7.0 bundles Clang 20, which cannot parse the
+      # __acquire_capability__ pack-expansion syntax introduced in
+      # libc++ 22's <mutex>. Pin libc++ to <22 until a castxml release
+      # builds against Clang 22+. Without this, every wrapped header
+      # fails at mutex:422.
+      - libcxx <22
       - if: env.get("ITK_CONDA_USE_CCACHE", default="0") == "1"
         then: ccache
       - if: build_platform != target_platform