Clarify Python autosubmission prerequisites

[ljones140]

Added note about .python-version file requirement for Python autosubmission.

Why:

Closes: https://github.com/github/docs-content/issues/19067

What's being changed (if available, include any code snippets, screenshots, or gifs):

Adding a line to python auto submission docs.

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.

[Copilot]

Pull Request Overview

This PR adds a clarification to the Python autosubmission documentation regarding the requirement for a .python-version file. The change helps users understand the prerequisite for Python version specification when using the autosubmission action.

• Adds a note explaining the .python-version file requirement for Python autosubmission

[github-actions]

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Source	Review	Production	What Changed
code-security/supply-chain-security/understanding-your-software-supply-chain/configuring-automatic-dependency-submission-for-your-repository.md	fpt ghec	fpt ghec

Key: fpt: Free, Pro, Team; ghec: GitHub Enterprise Cloud; ghes: GitHub Enterprise Server

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[github-actions]

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