[ci] Freeze emscripten / playwright version

1.51.0 seems to install incorrectly

Author: serge-sans-paille

.github/workflows/emscripten.yml

@@ -15,7 +15,7 @@ jobs:
         with:
             environment-name: xsimd
             create-args: >-
-                microsoft::playwright
+                microsoft::playwright=1.50.0
                 python
             init-shell: bash