Add an end-to-end test for Dijkstra transaction witnessing

[palas]

Context

This is the regression test for #1422: transaction assemble used to reject witness
files from eras after Conway, and the fix merged without its test because the test needs
dijkstra transaction commands to exist on master, which only happened in the PR below
this one.

How to trust this PR

• Test-only: zero changes to library or executable code
• The test passes
• It is a simple workflow

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff
• Changelog fragment added in .changes/

[Copilot]

Pull request overview

Adds a golden end-to-end regression test to ensure cardano-cli dijkstra transaction assemble can consume witness files produced by cardano-cli dijkstra transaction witness, covering the Dijkstra-era witness round-trip that previously failed (issue #1422).

Changes:

• Introduces a new golden property test that builds a raw tx body, produces a detached witness, then assembles a signed tx and asserts the resulting text-envelope era types.
• Registers the new test module in the cardano-cli-golden test-suite so it’s compiled and discovered.
• Adds a changelog fragment documenting the new test coverage.

Reviewed changes

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

File	Description
cardano-cli/test/cardano-cli-golden/Test/Golden/Dijkstra/Transaction/Assemble.hs	New golden E2E test for Dijkstra build-raw → witness → assemble, asserting expected text envelope types.
cardano-cli/cardano-cli.cabal	Adds the new Dijkstra test module to the golden test-suite module list.
.changes/20260828_214439_cardano-cli_palas_dijkstra_witnessing_test.yml	Changelog fragment noting the added Dijkstra witnessing regression test.

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