Fix warning silencer crashes when receiving DeprecationWarning objects

[verdimrc]

Issue #, if available: N/A

Description of changes: unbreak some cases where _warn() receives non-string objects such as DeprecationWarning objects.

Testing done: done

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[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
src/a2rl
__init__.py	21	1	95%	35
simulator.py	577	56	90%	456–458, 471, 537, 543, 559–594, 600, 912, 1011, 1026, 1036, 1041, 1057, 1075, 1097, 1123, 1144, 1150, 1167, 1171, 1177, 1187, 1194, 1217, 1223, 1302, 1309, 1364, 1371, 1377, 1384, 1387, 1498, 1514–1516, 1525, 1549, 1588, 1591
tokenizer.py	116	2	98%	64–65
utils.py	161	22	86%	51, 60–63, 74–76, 108, 147, 164, 179–181, 336–339, 475–484, 544, 558
src/a2rl/experimental/lightgpt
lr_decay.py	20	1	95%	30
model.py	116	2	98%	260, 263
simulator.py	35	1	97%	162
src/a2rl/mingpt
model.py	118	4	97%	57, 203, 208, 230
trainer.py	84	14	83%	50–51, 55–57, 108–111, 116, 124–126, 134, 140–141
TOTAL	1550	103	93%

Tests	Skipped	Failures	Errors	Time
234	0 💤	0 ❌	0 🔥	33.956s ⏱️

[verdimrc]

LGTM, despite pandas-1.5.0 breaks mypy checks.