CI: Consolidate CI to Python 3 and remove obsolete Python2 tests

[bernhardkaindl]

This is the CI part of consolidating xen-bugtool to Python3

Summary based on Sourcery (edited and updated)

Consolidate CI to Python 3 by removing obsolete Python 2 test workflows.
Update remaining jobs and scripts to use Python 3.

CI:

• Remove Python2 PyLint, pytest, and coverage jobs
• Switch Docker container tests to use alpine-python3
• Remove COVERALLS_PARALLEL flag and legacy Codecov/uploaders job
• Simplify Coveralls invocation and remove continue-on-error handling

Tests:

• Update integration test scripts to default to python3 instead of python2

Besides the review by GitHub CoPilot below, there is also a review by Sourcery (looks fine): xenserver-next#46 (review)

[Copilot]

Pull Request Overview

This PR consolidates the CI pipeline to Python 3 by removing obsolete Python 2 testing infrastructure and updating remaining components to use Python 3 exclusively.

• Removes Python 2 test jobs (PyLint, pytest, coverage) from GitHub Actions workflow
• Updates Docker container tests to use alpine-python3 instead of alpine-python2
• Updates integration test scripts to default to python3 instead of python2

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
.github/workflows/main.yml	Removes Python 2 CI jobs, updates container to alpine-python3, simplifies Coveralls setup
tests/integration/xenserver-config-systemd.sh	Changes default Python interpreter from python2 to python3, removes outdated comments
tests/integration/sar-file-collection.test.sh	Changes default Python interpreter from python2 to python3, fixes typo in comment

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[chunjiez]

I'm not experienced enough with the github CI test to comment on the update.

Roughly, the update looks good.