gh-35250: Fix doctests for nauty 2.8.6 output changes
    
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### 📚 Description

See #35157 and #34133.

This changes doctests to accomodate to changes in nauty output (which
are only used for debug purposes).

OTOH, there is a bug in the released nauty 2.8.6 which causes another
doctest failure reported in #35157. On a system with patched nauty 2.8.6
the current PR is good enough.

Leave #35157 open. To fix it a good option might be running `gentreeg 2`
at configure time and check the bug is not present so it's possible to
use 2.8.6 from system if it's been patched. In case it's useful, the
patch I'm using is https://gitweb.gentoo.org/repo/gentoo.git/plain/sci-
mathematics/nauty/files/nauty-2.8.6-gentreeg-gentourng.patch

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### ⌛ Dependencies
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URL: #35250
Reported by: Gonzalo Tornaría
Reviewer(s): David Coudert

src/sage/graphs/generators/families.py

@@ -3660,7 +3660,7 @@ def nauty_gentreeg(options="", debug=False):
 
         sage: gen = graphs.nauty_gentreeg("4", debug=True)
         sage: print(next(gen))
-        >A ...gentreeg Z=2:3 D=3 n=4
+        >A ...gentreeg ...
         sage: gen = graphs.nauty_gentreeg("4 -q", debug=True)
         sage: next(gen)
         ''
@@ -3687,7 +3687,7 @@ def nauty_gentreeg(options="", debug=False):
         sage: list(graphs.nauty_gentreeg("3 -x", debug=True))
         ['>E Usage: ...gentreeg [-D#] [-Z#:#] [-ulps] [-q] n [res/mod] ...
         sage: list(graphs.nauty_gentreeg("3", debug=True))
-        ['>A ...gentreeg Z=2:2 D=2 n=3\n', Graph on 3 vertices]
+        ['>A ...gentreeg ...\n', Graph on 3 vertices]
     """
     import shlex
     from sage.features.nauty import NautyExecutable

src/sage/graphs/graph_generators.py

@@ -965,7 +965,7 @@ def nauty_geng(self, options="", debug=False):
             ...
             ValueError: wrong format of parameter option
             sage: list(graphs.nauty_geng("-c3", debug=True))
-            ['>E Usage: ...geng [-cCmtfbd#D#] [-uygsnh] [-lvq] ...
+            ['>E Usage: ...geng ...\n']
             sage: list(graphs.nauty_geng("-c 3", debug=True))
             ['>A ...geng -cd1D2 n=3 e=2-3\n', Graph on 3 vertices, Graph on 3 vertices]
         """