Fix ordinal() suffix for negative integers

[zixuniaowu]

Problem

humanize.ordinal() returns the wrong suffix for every negative integer:

>>> ordinal(-1)
'-1th'   # should be '-1st'
>>> ordinal(-2)
'-2th'   # should be '-2nd'
>>> ordinal(-21)
'-21th'  # should be '-21st'

The docstring documents "Works for any integer", and negative inputs are clearly within the promised domain (invalid types fall back to str(value)), so the behavior contradicts the contract.

Root cause

The suffix digit is computed from value % 100 / value % 10. Python's % maps negative operands to non-negative residues (-1 % 10 == 9), so all negative numbers land in the "th" digit bucket. The -11/-12/-13/-111/-112/-113 inputs are "accidentally correct" and mask the defect.

Fix

Normalize the magnitude before computing the digit; the sign is still applied by the outer f-string:

magnitude = abs(value)
digit = 0 if magnitude % 100 in (11, 12, 13) else magnitude % 10

Also adds two doctest examples plus 12 parametrized negative-integer tests (covering the five genuinely wrong values -1/-2/-3/-21/-101 and the "accidentally correct" families that previously hid the bug).

Verification

• Pristine base (392aef7) with only the new tests: 5 failed, 25 passed — proves the defect exists upstream, not introduced by this change
• After the fix: 756 passed, 112 skipped (full suite), pytest --doctest-modules src/humanize/number.py: 8 passed (Python 3.12)

Base for this branch: 392aef7 (current main at time of branching, 2026-09-16).

[hugovk]

Duplicate of #405 and #321 and lots more.

Check for duplicates next time.