Trac #34792: Slight documentation update for modules built upon a FiniteRankFreeModule

After #34424 (merged in Sage 9.7.rc0), the documentation of
`TensorFreeModule`, `ExtPowerFreeModule` and `ExtPowerDualFreeModule`
should say that these classes inherit from
`FiniteRankFreeModule_abstract`, not `FiniteRankFreeModule`.

URL: https://trac.sagemath.org/34792
Reported by: egourgoulhon
Ticket author(s): Eric Gourgoulhon
Reviewer(s): Matthias Koeppe

Author: Release Manager

src/sage/tensor/modules/ext_pow_free_module.py

@@ -85,7 +85,7 @@ class ExtPowerFreeModule(FiniteRankFreeModule_abstract):
     `R`, where `n` is the rank of `M`.
     Accordingly, the class :class:`ExtPowerFreeModule` inherits from the
     class
-    :class:`~sage.tensor.modules.finite_rank_free_module.FiniteRankFreeModule`.
+    :class:`~sage.tensor.modules.finite_rank_free_module.FiniteRankFreeModule_abstract`.
 
     This is a Sage *parent* class, whose *element* class is
     :class:`~sage.tensor.modules.alternating_contr_tensor.AlternatingContrTensor`
@@ -465,7 +465,7 @@ class ExtPowerDualFreeModule(FiniteRankFreeModule_abstract):
     `R`, where `n` is the rank of `M`.
     Accordingly, the class :class:`ExtPowerDualFreeModule` inherits from
     the class
-    :class:`~sage.tensor.modules.finite_rank_free_module.FiniteRankFreeModule`.
+    :class:`~sage.tensor.modules.finite_rank_free_module.FiniteRankFreeModule_abstract`.
 
     This is a Sage *parent* class, whose *element* class is
     :class:`~sage.tensor.modules.free_module_alt_form.FreeModuleAltForm`.

src/sage/tensor/modules/tensor_free_module.py

@@ -29,7 +29,7 @@
 `T^{(k,l)}(M)` is itself a free module over `R`, of rank `n^{k+l}`, `n`
 being the rank of `M`. Accordingly the class :class:`TensorFreeModule`
 inherits from the class
-:class:`~sage.tensor.modules.finite_rank_free_module.FiniteRankFreeModule`.
+:class:`~sage.tensor.modules.finite_rank_free_module.FiniteRankFreeModule_abstract`.
 
 .. TODO::