gh-142302: Fix mkstemp() documentation: clarify file descriptor inheritance behavior

[raixyzaditya]

Description

Fixes the misleading documentation for tempfile.mkstemp() regarding file descriptor inheritance.

The current documentation states "The file descriptor is not inherited by child processes," which is incomplete and misleading.

What was wrong

The file descriptor created by mkstemp() is inherited by child processes created via fork(). The close-on-exec flag (O_CLOEXEC), when available, only prevents inheritance across exec() calls, not fork() calls.

Changes made

Updated the documentation to accurately describe the inheritance behavior:

• Clarifies that O_CLOEXEC only affects exec() calls
• Notes that the fd is still inherited by forked child processes
• Maintains technical accuracy while being clear for users

Testing

Verified the documentation builds correctly:

cd Doc
make html

Related Issue

Fixes #142302

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📚 Documentation preview 📚: https://cpython-previews--142338.org.readthedocs.build/

• Issue: Tempfile.mkstemp file descriptor issue #142302

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[picnixz]

Please sign the CLA and address the CI issues. In addition, please wait for the maintainer to confirm that the documentation should be changed like that.

[raixyzaditya]

Thank you for your review
CLA: I have signed the CLA.
CI Issues: All tests are now passing. The CI issues have been resolved.
Documentation Change: I'm happy to wait for maintainer confirmation on the wording. The current documentation states "The file descriptor is not inherited by child processes," which is misleading since:

• The fd IS inherited by forked child processes
• Only exec() calls are affected by O_CLOEXEC (when available)
• This has been verified empirically in production code
  I'm open to alternative wording suggestions if the current approach needs adjustment. Please let me know if there's a preferred way to clarify this behavior.