[3.12] docs: fix grammar in isolating-extensions.rst (GH-108037) (#108218)

docs: fix grammar in isolating-extensions.rst (GH-108037)
(cherry picked from commit 47022a0)

Co-authored-by: David Lechner <[email protected]>

Author: miss-islington

Doc/howto/isolating-extensions.rst

@@ -64,7 +64,7 @@ Enter Per-Module State
 
 Instead of focusing on per-interpreter state, Python's C API is evolving
 to better support the more granular *per-module* state.
-This means that C-level data is be attached to a *module object*.
+This means that C-level data should be attached to a *module object*.
 Each interpreter creates its own module object, keeping the data separate.
 For testing the isolation, multiple module objects corresponding to a single
 extension can even be loaded in a single interpreter.