gh-36862: Fix one doctest for giac 1.9.0-73

With giac 1.9.0-73 the output of a `symbolic_sum()` test changes. Note
that both answers are correct, and it's not clear that one is "better"
than the other...

I managed to find a way to avoid trouble (by sending the output through
`factor()`) so the output is the same with latest giac and earlier giac.

However, fixing doctests keeps getting harder (I mean: making sure the
same doctest works for different releases of dependencies). I don't have
a good idea on how to improve the situation.

### 📝 Checklist

- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.

URL: #36862
Reported by: Gonzalo Tornaría
Reviewer(s): Matthias Köppe

build/pkgs/configure/checksums.ini

@@ -1,4 +1,4 @@
 tarball=configure-VERSION.tar.gz
-sha1=60efc2b1ac7c0dcd9175cbfad5beefaf8969f24f
-md5=0dc99ff8479a481293e59816a5d21488
-cksum=2783976116
+sha1=5bb6e594b35fce9bc66e06f620018bd18eb8346e
+md5=33c8854fa8d6f356c99ebfc55c2cf884
+cksum=1833053275

build/pkgs/configure/package-version.txt

@@ -1 +1 @@
-f66d283d487c6f8bcee6e135c93c5613796ce9e2
+e8571725a77eee05f130807f4638ad9043412d52

src/sage/calculus/calculus.py

@@ -568,8 +568,8 @@ def symbolic_sum(expression, v, a, b, algorithm='maxima', hold=False):
 
     An example of this summation with Giac::
 
-        sage: symbolic_sum(1/(1+k^2), k, -oo, oo, algorithm='giac')
-        (pi*e^(2*pi) - pi*e^(-2*pi))/(e^(2*pi) + e^(-2*pi) - 2)
+        sage: symbolic_sum(1/(1+k^2), k, -oo, oo, algorithm='giac').factor()
+        pi*(e^(2*pi) + 1)/((e^pi + 1)*(e^pi - 1))
 
     The same summation is solved by SymPy::