Follow-up of #6442

• A minimal code snippet that reproduces the bug:

  print("{0:.{prec}g}".format(1.23, prec=15))

• The command you invoked (e.g., ruff /path/to/file.py --fix), ideally including the --isolated flag:

  $ ruff --select PLE1300 file.py --isolated
  file.py:1:7: PLE1300  Unsupported format character 'g'
  Found 1 error.
  $ 
  

• The current Ruff version (ruff --version).

  $ ruff --version
  ruff 0.0.285
  $