Remove the test-specific Docker network

[MakisH]

Now that multiple GitHub Actions runners run on the same system, the approach of pruning Docker networks (#820) can lead to race conditions. The same applies to when running tests in parallel (#789).

This PR replaces the call to docker network prune (before and after the test) to a docker network ls filtered by working directory, followed by a docker network rm with the respective id. This is executed only after the test, as cleanup.

Testing in https://github.com/precice/tutorials/actions/runs/36738197148 - seems to work: networks are not accumulated.

[Copilot]

Copilot review overview

🟡 Changes recommended

Network discovery is nonfunctional, removal errors are hidden, and failed tests bypass cleanup.

Review effort: Balanced
Findings: 1 · 2 · 1

Open (4)

• Docker network listing passes unsupported shell pipeline arguments · New
• Failed tests bypass cleanup and leak Docker networks · New
• Reference-result failures bypass network cleanup · New
• Fix subject-verb agreement and Docker capitalization · New

What changed in this PR

Replaces global Docker network pruning with per-system-test network cleanup to avoid parallel-run races.

Changes:

• Adds targeted Docker network discovery and removal.
• Runs cleanup after tests and updates the changelog.

File	Description
tests/​systemtests/​Systemtest.py	Implements targeted network cleanup.
changelog-entries/​820.md	Updates the cleanup release note.

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[Copilot]

Copilot review overview

🟡 Changes recommended

The filter cannot find Compose networks, and destructor-based cleanup is deferred and unreliable.

Review effort: Balanced
Findings: 2 · 1 · 1

Open (4)

• Network filter does not match Compose-created networks · New
• Run network cleanup deterministically after each test · New
• Handle network removal failures · New
• Capitalize Docker consistently · New

Resolved since last review (4)

• Docker network listing passes unsupported shell pipeline arguments
• Reference-result failures bypass network cleanup
• Failed tests bypass cleanup and leak Docker networks
• Fix subject-verb agreement and Docker capitalization

[Copilot]

Copilot review overview

🟡 Changes recommended

Concurrent runners can share a project identifier, allowing one test to remove another test’s network.

Review effort: Balanced
Findings: 1 · 1

Open (2)

• Use a unique Compose project identifier per execution · New
• Handle docker network ls command failures · New

Resolved since last review (4)

• Run network cleanup deterministically after each test
• Network filter does not match Compose-created networks
• Handle network removal failures
• Capitalize Docker consistently