ci: Use Python 3.12 to compute benchmarks

[edgarrmondragon]

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📚 Documentation preview 📚: https://meltano-sdk--2134.org.readthedocs.build/en/2134/

[codspeed-hq]

CodSpeed Performance Report

Merging #2134 will degrade performances by 26.19%

_{Comparing ci/py3.12-benches (902d8ec) with main (b442647)}

Summary

❌ 6 regressions

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	ci/py3.12-benches	Change
❌	test_bench_deserialize_json	107 ms	124 ms	-13.7%
❌	test_bench_validate_record_with_schema	442.1 ms	599 ms	-26.19%
❌	test_bench_format_message	249.9 ms	279 ms	-10.41%
❌	test_bench_simple_map_transforms	2.5 s	3.3 s	-23.51%
❌	test_bench_parse_timestamps_in_record	50.6 ms	65.9 ms	-23.2%
❌	test_bench_validate_and_parse	494.2 ms	668.9 ms	-26.13%