Always use python to run the pexpect interface

[antonio-rojas]

sage-ipython is no longer available in the meson build

Fixes #39869

[github-actions]

Documentation preview for this PR (built with commit a6b5fa4; changes) is ready! 🎉
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[tobiasdiez]

LGTM, thanks!

[vbraun]

I'm getting

Doctesting 1 file.
sage -t --long --warn-long 30.0 --random-seed=123 src/sage/misc/randstate.pyx
**********************************************************************
File "src/sage/misc/randstate.pyx", line 130, in sage.misc.randstate
Failed example:
    s = ZZ(subsage('initial_seed()'))
Exception raised:
    Traceback (most recent call last):
      File "/home/release/Sage/src/sage/doctest/forker.py", line 730, in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "/home/release/Sage/src/sage/doctest/forker.py", line 1154, in compile_and_execute
        exec(compiled, globs)
      File "<doctest sage.misc.randstate[30]>", line 1, in <module>
        s = ZZ(subsage('initial_seed()'))
               ^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/home/release/Sage/src/sage/interfaces/sage0.py", line 239, in __call__
        return SageElement(self, x)
               ^^^^^^^^^^^^^^^^^^^^
      File "/home/release/Sage/src/sage/interfaces/expect.py", line 1518, in __init__
        self._name = parent._create(value, name=name)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/home/release/Sage/src/sage/interfaces/interface.py", line 520, in _create
        self.set(name, value)
      File "/home/release/Sage/src/sage/interfaces/sage0.py", line 319, in set
        raise TypeError("Error executing code in Sage\nCODE:\n\t%s\nSage ERROR:\n\t%s" % (cmd, out))
    TypeError: Error executing code in Sage
    CODE:
    	sage0=initial_seed()
    Sage ERROR:
    	Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
        sage0=initial_seed()
              ^^^^^^^^^^^^
    NameError: name 'initial_seed' is not defined
**********************************************************************

[tobiasdiez]

Now one test has timeout issues (see meson ci).

@vbraun would it be possible to preinstall a suitable python on the bots so that they don't use sage's python build?

[antonio-rojas]

Should be fine now, please review again