[deps] Update django-pipeline requirement from ~=3.1 to ~=4.0 in /images/openwisp_base

[dependabot]

Updates the requirements on django-pipeline to permit the latest version.

Release notes

Sourced from django-pipeline's releases.

4.0.0

• Drop support for Python 3.8
• Confirm support for Django 5.1 and drop support for Django 3.2
• Use pyproject.toml

Changelog

Sourced from django-pipeline's changelog.

4.0.0

• Drop support for Python 3.8
• Confirm support for Django 5.1 and drop support for Django 3.2
• Use pyproject.toml

3.1.0

• Replace deprecated .warn method with .warning
• Update sourcemap paths when concatenating source files
• Ensure correct compiler error styling and strip ANSI escape sequences

3.0.0

• Use Pypy 3.10
• Drop support for Python 3.7
• Drop support for Django 2
• Add Python 3.12 support
• Add Django 4.2 support
• Add Django 5.0 support

2.1.0

• Update README.rst and add Pipeline overview image.
• Add TypeScript compiler support.
• Drop support for manifesto package.
• Add support for Python 3.11 and Django 4.1

2.0.9

• Fixed some typos in the docs.
• Fixed string type of errors reported from compilers and compressors.
• Updated github actions matrix for host and django support.
• Updated github actions configuration to use modern versions of third-party actions.
• Improved the packager to copy files to (S3) storage if it does not exist (#502).

2.0.8

• Added Django 4.0 compatibility. Thanks to @​kevinmarsh (#760)
• Add tests for Django 4.0, Python 3.9 and Python 3.10. Thank to @​kevinmarsh (#739)

... (truncated)

Commits

• f36dbe0 use release/v1 for pypi publish github action (#829)
• c5ad9cc Update version to release v4 (#827)
• 633bd81 Remove unused comments (#828)
• a8e8cf7 Add dependabot monthly update for github actions (#826)
• 7631f71 Upgrade github actions (#825)
• 83a0ae7 Replace setup.py with pyproject.toml (#824)
• 1e8bfa8 Replace node-sass with sass in test dependencies (#823)
• f7389ac Confirm support of Django 5.1 and drop Django 3.2 (#822)
• 2832bda Drop Python 3.8 support (#821)
• 00ece40 [pre-commit.ci] pre-commit autoupdate
• Additional commits viewable in compare view

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[pandafy]

@dependabot rebase

[nemesifier]

@dependabot recreate

[nemesifier]

@dependabot recreate

[dependabot]

Looks like django-pipeline is up-to-date now, so this is no longer needed.