gh-126105: Fix crash in `ast` module, when `._fields` is deleted (#12… #625

Job	Run time
Change detection / Compute changed files	7s
Check if generated files are up to date	3m 2s
Check if Autoconf files are up to date	21s
Docs	0s
Ubuntu SSL tests with OpenSSL (ubuntu-22.04, 3.0.15)	2m 20s
Windows MSI${{ '' }}	0s
Hypothesis tests on Ubuntu	6m 6s
Ubuntu SSL tests with OpenSSL (ubuntu-22.04, 3.1.7)	2m 31s
Ubuntu SSL tests with OpenSSL (ubuntu-22.04, 3.2.3)	2m 34s
Address sanitizer (ubuntu-22.04)	10m 34s
Ubuntu SSL tests with OpenSSL (ubuntu-22.04, 3.3.2)	2m 30s
CIFuzz	0s
Thread sanitizer / Thread sanitizer	5m 56s
WASI / build and test	7m 24s
Thread sanitizer (free-threading) / Thread sanitizer	8m 40s
Windows / build (arm64)	3m 35s
Windows (free-threading) / build (arm64)	2m 13s
Windows / build and test (Win32)	16m 37s
Windows (free-threading) / build and test (Win32)	24m 28s
Windows / build and test (x64)	15m 59s
Windows (free-threading) / build and test (x64)	23m 59s
macOS / build and test (macos-13)	15m 19s
macOS / build and test (macos-14)	8m 28s
macOS (free-threading) / build and test (macos-14)	9m 41s
Ubuntu / build and test (ubuntu-22.04)	7m 52s
Ubuntu (free-threading) / build and test (ubuntu-22.04)	10m 57s
All required checks pass	3s
	3h 11m 16s

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