sagemathgh-38627: Require weaker Sphinx dependency for sagelib

    
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The version constraint added in
sagemath#38549 broke the conda ci workflow
and added an unnecessarily strict version constraint for sphinx as a
dependency of sagelib (as opposed to sage-the-docs).

This is fixed by providing the old version constraint for sphinx in
`setup.cfg`, but with `v8` now allowed.

Alternatively, the stricter version constraint should only be added to
the sage-the-docs package.

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### ⌛ Dependencies

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URL: sagemath#38627
Reported by: Tobias Diez
Reviewer(s): François Bissey

src/setup.cfg.m4

@@ -33,7 +33,7 @@ dnl From Makefile.in: SAGERUNTIME
     SPKG_INSTALL_REQUIRES_ipython
     SPKG_INSTALL_REQUIRES_pexpect
 dnl From Makefile.in: DOC_DEPENDENCIES
-    SPKG_INSTALL_REQUIRES_sphinx
+    sphinx >=5.2, <9
     SPKG_INSTALL_REQUIRES_networkx
     SPKG_INSTALL_REQUIRES_scipy
     SPKG_INSTALL_REQUIRES_sympy