tests/test_pixmap.py: fix pyodide failure with mupdf-1.26.x.

Author: julian-smith-artifex-com

tests/test_pixmap.py

@@ -522,7 +522,7 @@ def test_4435():
     with pymupdf.open(path) as document:
         page = document[2]
         print(f'Calling page.get_pixmap().', flush=1)
-        if os.environ.get('PYODIDE_ROOT'):
+        if pymupdf.mupdf_version_tuple >= (1, 27) and os.environ.get('PYODIDE_ROOT'):
             # 2025-11-07: Expect alloc failure.
             try:
                 pixmap = page.get_pixmap(alpha=False, dpi=120)