tests: Avoid aliased Functions in a single Operator in test_w_data

`f` and `g` share their buffer, but the generated code declares their
pointers `restrict`, so fusing `Eq(f, f+1)` and `Eq(g, g+1)` into one
Operator lets the compiler hoist the load from `g` above the store to
`f`. gcc 13 and 14 do exactly that and increment by one instead of two,
which is why the test failed on some CI runners and not others. Use one
Operator per Function instead.

Author: mloubout

tests/test_data.py

@@ -2187,8 +2187,13 @@ def _w_data(self):
 
         check = np.array(f.data_with_halo[1:-1, 1:-1])
 
-        # Update both
-        Operator([Eq(f, f+1), Eq(g, g+1)])()
+        # Update both. NOTE: `f` and `g` share their buffer, but the generated
+        # code says otherwise -- the pointers are `restrict` qualified -- so
+        # they have to be updated by separate Operators. Fusing the two Eqs
+        # would leave the compiler free to hoist the load from `g` above the
+        # store to `f`, yielding an increment of one rather than two
+        Operator(Eq(f, f+1))()
+        Operator(Eq(g, g+1))()
         assert np.all(f.data_with_halo == g.data_with_halo)
         # Check that it was incremented by two
         check += 2