Skip tests for g/G format types in CPython 3.8

$ python3.9
    Python 3.9.19+ (heads/3.9:3f5d9d12c7, Aug 29 2024, 13:17:09)
    [GCC 12.2.0] on linux
    Type "help", "copyright", "credits" or "license" for more information.
    >>> format(240605919345005.0, '.14g')
    '2.40605919345e+14'
    $ python3.8
    Python 3.8.19+ (heads/3.8:e319f774f9, Aug 29 2024, 12:59:09)
    [GCC 12.2.0] on linux
    Type "help", "copyright", "credits" or "license" for more information.
    >>> format(240605919345005.0, '.14g')
    '2.4060591934500e+14'

mpmath/tests/test_format.py

@@ -477,6 +477,8 @@ def test_mpf_floats_bulk(fmt, x):
     if not x and math.copysign(1, x) == -1:
         return  # skip negative zero
     spec = read_format_spec(fmt)
+    if sys.version_info < (3, 9) and spec['type'] in ('g', 'G'):
+        pytest.skip("CPython has incompatible g/G formatting in 3.8 and 3.9+")
     if not spec['type'] and spec['precision'] < 0 and math.isfinite(x):
         # The mpmath could choose a different decimal
         # representative (wrt CPython) for same binary
@@ -498,6 +500,8 @@ def test_mpc_complexes(fmt, z):
             or (not z.imag and math.copysign(1, z.imag) == -1)):
         return  # skip negative zero
     spec = read_format_spec(fmt)
+    if sys.version_info < (3, 9) and spec['type'] in ('g', 'G'):
+        pytest.skip("CPython has incompatible g/G formatting in 3.8 and 3.9+")
     if spec['precision'] < 0 and any(math.isfinite(_) for _ in [z.real, z.imag]):
         # The mpmath could choose a different decimal
         # representative (wrt CPython) for same binary