gh-36183: `sage.misc.sageinspect`: fix doctest warnings due to modularisation
    
We fix the following doctest warnings:
```
sage -t --long --warn-long 30.7 --random-
seed=263240816384135969928803999009622073573
src/sage/misc/sageinspect.py
**********************************************************************
File "src/sage/misc/sageinspect.py", line 1627, in
sage.misc.sageinspect.sage_getargspec
Warning: Variable 'Foo' referenced here was set only in doctest marked
'# needs sage.misc.cython'
    sage_getargspec(Foo.join)
**********************************************************************
File "src/sage/misc/sageinspect.py", line 1629, in
sage.misc.sageinspect.sage_getargspec
Warning: Variable 'Bar' referenced here was set only in doctest marked
'# needs sage.misc.cython'
    sage_getargspec(Bar.join)
**********************************************************************
File "src/sage/misc/sageinspect.py", line 1631, in
sage.misc.sageinspect.sage_getargspec
Warning: Variable 'Bar' referenced here was set only in doctest marked
'# needs sage.misc.cython'
    sage_getargspec(Bar.meet)
    [353 tests, 32.04 s]
```

These are (currently) the only warnings I see when running `./sage -t
--long src/sage/misc/`.

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URL: #36183
Reported by: David Coudert
Reviewer(s): Frédéric Chapoton

Author: Release Manager

src/sage/misc/sageinspect.py

@@ -1614,7 +1614,8 @@ def foo(x, a='\')"', b={not (2+1==3):'bar'}): return
 
     The following was fixed in :trac:`16309`::
 
-        sage: cython(                                                                   # needs sage.misc.cython
+        sage: # needs sage.misc.cython
+        sage: cython(
         ....: '''
         ....: class Foo:
         ....:     @staticmethod