Apply suggestions from code review

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Author: ZeroIntensity

peps/pep-0797.rst

@@ -24,7 +24,7 @@ the interpreter is shutting down using a simulated garbage collection.
 
 For example:
 
-.. code-block:: C
+.. code-block:: c
 
     static PyObject *
     my_singleton_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
@@ -178,7 +178,7 @@ Immortality Has No Impact on Reference Counting Performance
 
 If the primary issue with cross-interpreter reference counting is thread-safety,
 why not make reference counting atomic? Unfortunately, atomic operations are
-slower than their non-atomic counterparts, so this would hurt overalll
+slower than their non-atomic counterparts, so this would hurt overall
 performance. :pep:`703` managed to solve this issue using biased reference
 counting, splitting the reference count field into two, but at the cost of
 breaking the stable C API. Atomic reference counting on its own also doesn't
@@ -395,7 +395,7 @@ The initial problem to solve with deallocating immortal objects is that they
 can run finalizers, which might reference other immortal objects. Imagine a
 case where there are two immortal objects: A, and B. Object B has a finalizer
 that references object A, and object A has a finalizer that references object
-B. The solution is to simply run their finalizer seperately from their
+B. The solution is to simply run their finalizer separately from their
 deallocator.
 
 Temporary Mortalization for Finalizers