gh-125873: Improve error message when PYTHONHOME is invalid #130603

Job	Run time
Change detection / Compute changed files	9s
Check if Autoconf files are up to date	21s
Address sanitizer	30s
Ubuntu SSL tests with OpenSSL (ubuntu-22.04, 3.0.15)	27s
Ubuntu SSL tests with OpenSSL (ubuntu-22.04, 3.1.7)	39s
Windows MSI${{ '' }}	0s
Check if generated files are up to date	28s
Ubuntu SSL tests with OpenSSL (ubuntu-22.04, 3.2.3)	27s
CIFuzz (address)	25s
Ubuntu SSL tests with OpenSSL (ubuntu-22.04, 3.3.2)	39s
CIFuzz (undefined)	25s
Hypothesis tests on Ubuntu	27s
CIFuzz (memory)	26s
Thread sanitizer / Thread sanitizer	38s
Thread sanitizer (free-threading) / Thread sanitizer	40s
WASI / build and test	39s
Windows / build (arm64)	33s
Windows (free-threading) / build (arm64)	23s
Windows / build and test (Win32)	24s
Windows (free-threading) / build and test (Win32)	33s
Windows / build and test (x64)	30s
Windows (free-threading) / build and test (x64)	30s
macOS (free-threading) / build and test (ghcr.io/cirruslabs/macos-runner:sonoma)	15s
macOS / build and test (ghcr.io/cirruslabs/macos-runner:sonoma)	11s
macOS / build and test (macos-13)	30s
Ubuntu / build and test (ubuntu-22.04)	24s
Ubuntu (free-threading) / build and test (ubuntu-22.04)	26s
Docs / Docs	37s
Docs / Docs (Oldest Sphinx)	27s
Docs / Doctest	32s
All required checks pass	2s
	13m 37s

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