tests: mark and add skips (#2524)

* tests: mark and add skips

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* fix comment

---------

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>
Co-authored-by: Matthieu Darbois <mayeut@users.noreply.github.com>

test/test_pyodide.py

@@ -1,4 +1,5 @@
 import contextlib
+import os
 import subprocess
 import sys
 import textwrap
@@ -9,6 +10,12 @@ from cibuildwheel.util.file import CIBW_CACHE_PATH
 
 from . import test_projects, utils
 
+pytestmark = pytest.mark.pyodide
+
+CIBW_PLATFORM = os.environ.get("CIBW_PLATFORM", "pyodide")
+if CIBW_PLATFORM != "pyodide":
+    pytest.skip(f"{CIBW_PLATFORM=}", allow_module_level=True)
+
 basic_project = test_projects.new_c_project()
 basic_project.files["check_node.py"] = r"""
 import sys