explicitly resolve Python for pex run/package #25375

Job	Run time
Classify changes	4s
Bootstrap Pants, test Rust (Linux-ARM64)	1m 48s
Bootstrap Pants, test Rust (macOS13-x86_64)	3m 17s
Build wheels (Linux-ARM64)	0s
Bootstrap Pants, test and lint Rust (Linux-x86_64)	2m 54s
Build wheels (macOS13-x86_64)	0s
Build wheels (Linux-x86_64)	0s
Ensure PR has release notes	4s
Build wheels (macOS14-ARM64)	0s
Test Python (Linux-ARM64)	9m 40s
Lint Python and Shell	2m 42s
Test Python (Linux-x86_64) Shard 0/10	15m 34s
Test Python (Linux-x86_64) Shard 1/10	13m 21s
Test Python (Linux-x86_64) Shard 2/10	17m 52s
Test Python (Linux-x86_64) Shard 3/10	11m 32s
Test Python (Linux-x86_64) Shard 5/10	15m 0s
Test Python (Linux-x86_64) Shard 4/10	34m 28s
Test Python (Linux-x86_64) Shard 6/10	8m 41s
Test Python (Linux-x86_64) Shard 7/10	17m 27s
Test Python (Linux-x86_64) Shard 8/10	8m 39s
Test Python (Linux-x86_64) Shard 9/10	7m 26s
Test Python (macOS13-x86_64)	15m 14s
Set Merge OK	0s
Merge OK	1s
	3h 5m 44s

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