Doc: Fix suggested usage of `-X gil=0` in the glossary (#125366)

Currently, the "global interpreter lock" entry in the glossary mentions
that `-X gil 0` can be used to disable the GIL [1]. However, this is
invalid; the correct usage should be `-X gil=0`.

    $ python -X gil 0 -c 'print("Hello, world")'
    Fatal Python error: config_read_gil: PYTHON_GIL / -X gil must be "0" or "1"
    Python runtime state: preinitialized

    $ python -X gil=0 -c 'print("Hello, world")'
    Hello, world

[1]: https://docs.python.org/3/using/cmdline.html#cmdoption-X

Signed-off-by: Ruoyu Zhong <[email protected]>