gh-157137: Mark the PEP 820 soft deprecations as 3.15, not next

All seven were already in the tree at v3.15.0b1, and Doc/whatsnew/3.15.rst
lists exactly those functions as 3.15 soft deprecations. The 3.15.0b1
commit rewrote 84 ":: next" tags and none of the soft-deprecated:: ones.

Author: fedonman

Doc/c-api/module.rst

@@ -853,7 +853,7 @@ struct:
 
    .. versionadded:: 3.5
 
-   .. soft-deprecated:: next
+   .. soft-deprecated:: 3.15
 
       Prefer :c:func:`PyModule_FromSlotsAndSpec` in new code.
 
@@ -877,7 +877,7 @@ struct:
 
    .. versionadded:: 3.5
 
-   .. soft-deprecated:: next
+   .. soft-deprecated:: 3.15
 
       Prefer :c:func:`PyModule_FromSlotsAndSpec` in new code.
 
@@ -887,7 +887,7 @@ struct:
 
    .. versionadded:: 3.5
 
-   .. soft-deprecated:: next
+   .. soft-deprecated:: 3.15
 
       To run a module's own execution slots, prefer :c:func:`PyModule_Exec`,
       which works on modules that were not created from a

Doc/c-api/type.rst

@@ -828,7 +828,7 @@ They will continue to work, but new features will be added as slots for
 
    .. versionadded:: 3.12
 
-   .. soft-deprecated:: next
+   .. soft-deprecated:: 3.15
 
       Prefer :c:func:`PyType_FromSlots` in new code.
 
@@ -859,7 +859,7 @@ They will continue to work, but new features will be added as slots for
       Creating classes whose metaclass overrides
       :c:member:`~PyTypeObject.tp_new` is no longer allowed.
 
-   .. soft-deprecated:: next
+   .. soft-deprecated:: 3.15
 
       Prefer :c:func:`PyType_FromSlots` in new code.
 
@@ -885,7 +885,7 @@ They will continue to work, but new features will be added as slots for
       Creating classes whose metaclass overrides
       :c:member:`~PyTypeObject.tp_new` is no longer allowed.
 
-   .. soft-deprecated:: next
+   .. soft-deprecated:: 3.15
 
       Prefer :c:func:`PyType_FromSlots` in new code.
 
@@ -910,7 +910,7 @@ They will continue to work, but new features will be added as slots for
       Creating classes whose metaclass overrides
       :c:member:`~PyTypeObject.tp_new` is no longer allowed.
 
-   .. soft-deprecated:: next
+   .. soft-deprecated:: 3.15
 
       Prefer :c:func:`PyType_FromSlots` in new code.