bump 3.12 to 3.13 in readme #1020

Job	Run time
docs	1m 49s
Rust unit tests (ubuntu-latest)	2m 18s
Rustfmt	8s
Rust unit tests (macos-latest)	2m 11s
lint	1m 29s
Rust unit tests (windows-latest)	4m 38s
test (macos-latest, 3.9)	4m 23s
typecheck	1m 16s
test (macos-latest, 3.10)	4m 8s
test (macos-latest, 3.11)	3m 56s
test (macos-latest, 3.12)	5m 13s
test (macos-latest, 3.13)	4m 39s
test (ubuntu-latest, 3.9)	5m 58s
test (ubuntu-latest, 3.10)	5m 52s
test (ubuntu-latest, 3.11)	6m 19s
test (ubuntu-latest, 3.12)	8m 56s
test (ubuntu-latest, 3.13)	8m 57s
test (windows-latest, 3.9)	8m 40s
test (windows-latest, 3.10)	8m 35s
test (windows-latest, 3.11)	11m 4s
test (windows-latest, 3.12)	11m 42s
test (windows-latest, 3.13)	10m 52s
	2h 3m 3s

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