gh-94772: Fix off-by-one error in Windows launcher

[pfmoore]

Fixes #94772.

• Issue: Python 3.11.0b4 - py launcher fails when running a script with a shebang line #94772

[pelson]

Was just doing a fly-by look at the implementation out of curiosity. Since I'm here, I noticed that there doesn't appear to be a single test which checks a shebang without a space before the first command (e.g. #!/usr/bin/env python). Since this is the common case in Unix (though the leading space is peppered throughout PEP 397), I would recommend to add such a test.

Quoting wikipedia on the issue:

It has been claimed[20] that some old versions of Unix expect the normal shebang to be followed by a space and a slash (#! /), but this appears to be untrue;[21] rather, blanks after the shebang have traditionally been allowed, and sometimes documented with a space (see the 1980 email in history section below)

[pfmoore]

+1 on more tests, and the one you suggest seems reasonable. Ideally, I'd test a variety of scripts using parametrised tests, but I'm not sure how to do those in unittest...

The main focus of this PR is to fix the regression in the launcher, so I'd suggest extra tests get added in a follow-up PR, though.

[miss-islington]

Thanks @pfmoore for the PR, and @zooba for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖

[bedevere-bot]

GH-94896 is a backport of this pull request to the 3.11 branch.

[pfmoore]

Thanks @zooba for merging this.