Add ENV variable to skip network test

[janezpodhostnik]

Description

When making a nix derivation for flow-cli I noticed that some tests use networking. This fails in sandboxed environments. I added a SKIP_NETWORK_TESTS env variable to optionally skip them.

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For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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