docs: update tox Python version examples

[sueun-dev]

What type of PR is this? (check all applicable)

• Refactor
• Feature
• Bug Fix
• Optimization
• Documentation Update
• Other

Description

The testing section still showed tox -e py37, but Python 3.7 support has been removed. This updates the English and Spanish README examples to use py38, matching the current tox.ini env list and python_requires >=3.8 package metadata.

Related Issues

None.

PR checklist

Before submitting this pull request, I have done the following:

• Read the contributing guidelines
• Ran relevant local checks
• Added my changes to the CHANGES file

Added/updated tests?

Current repository has 100% test coverage.

• Yes
• No, docs-only example update.
• I need help with writing tests

Checked:

• tox list
• tox -e py37 --notest
• python setup.py check --metadata --restructuredtext
• python -m pytest . --asyncio-mode=auto
• pre-commit run --all-files
• PIP_CONSTRAINT=/tmp/responses-constraints.txt tox -r -e py39
• git diff --check

Note: unconstrained tox -e py39 hit urllib3's NotOpenSSLWarning on Apple's LibreSSL-backed Python 3.9 before tests were collected. The constrained tox run used urllib3<2, which is still inside the package's declared dependency range, and passed.

[markstory]

Thank you 🎉