Change NAMESPACE_* macros into PYBIND11_NAMESPACE_* (#2283)

* Change NAMESPACE_BEGIN and NAMESPACE_END macros into PYBIND11_NAMESPACE_BEGIN and PYBIND11_NAMESPACE_END

* Fix sudden HomeBrew 'python not installed' error

* Sweep difference in 'Class.__init__() must be called when overriding __init__' error message between CPython and PyPy under the rug

* Homebrew updated to 3.8 yesterday.

Co-authored-by: Henry Schreiner <HenrySchreinerIII@gmail.com>
diff --git a/tests/test_copy_move.cpp b/tests/test_copy_move.cpp
index 98d5e0a..0f698bd 100644
--- a/tests/test_copy_move.cpp
+++ b/tests/test_copy_move.cpp
@@ -68,8 +68,8 @@
 
     int value;
 };
-NAMESPACE_BEGIN(pybind11)
-NAMESPACE_BEGIN(detail)
+PYBIND11_NAMESPACE_BEGIN(pybind11)
+PYBIND11_NAMESPACE_BEGIN(detail)
 template <> struct type_caster<MoveOnlyInt> {
     PYBIND11_TYPE_CASTER(MoveOnlyInt, _("MoveOnlyInt"));
     bool load(handle src, bool) { value = MoveOnlyInt(src.cast<int>()); return true; }
@@ -97,8 +97,8 @@
     operator CopyOnlyInt&() { return value; }
     template <typename T> using cast_op_type = pybind11::detail::cast_op_type<T>;
 };
-NAMESPACE_END(detail)
-NAMESPACE_END(pybind11)
+PYBIND11_NAMESPACE_END(detail)
+PYBIND11_NAMESPACE_END(pybind11)
 
 TEST_SUBMODULE(copy_move_policies, m) {
     // test_lacking_copy_ctor