gh-136879: Make os.spawn* arg signatures consistent with os.exec*

[kovan]

Summary

• Updates os.spawnl, spawnle, spawnlp, and spawnlpe function signatures to show arg0, arg1, ... explicitly
• This matches the documentation style of the os.execl family of functions

Before: spawnl(mode, path, ...)
After: spawnl(mode, path, arg0, arg1, ...)

Source verification

• Verified in Lib/os.py that both exec* and spawn* use *args parameter

Test plan

• make check passed

🤖 Generated with Claude Code

• Issue: os.exec* and os.spawn* functions describe their arg* parameters differently #136879

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📚 Documentation preview 📚: https://cpython-previews--144458.org.readthedocs.build/

[picnixz]

Strictly speaking, this is not the signature at runtime. At runtime, the signature is spawnl(mode, path, *args) so the ... part is correct. So I think we should first decide on the issue how we want to document the expanded args. Do we want to explicitly document spawnl(mode, path, arg0, arg1, ...), or spawnl(mode, path, arg0, ...) or simply specify that args must be non-empty with args[0] being the program name by convention? since we did not discuss yet about it, I am closing the PR otherwise it will be kept open for too long.

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