Assert the source archive itself is absent in testNoSources

[kratos0718]

Fixes #308

Problem

Both testNoSources cases assert that no archive was produced like this:

final File expectedFile = getTestTargetDir("project-005");
assertFalse(
        expectedFile.exists(),
        "Source archive should not have been created[" + expectedFile.getAbsolutePath() + "]");

getTestTargetDir returns the project's target directory, not the artifact. So the assertion never inspects the jar named in its own failure message — it is bound to whether a directory happens to exist rather than to whether the mojo produced an archive. A directory left behind by earlier build scaffolding, or created for unrelated reasons, is enough to change the outcome, and conversely the check cannot notice a stray jar inside a directory that does exist.

Fix

Assert the specific artifact instead, reusing the helpers already on AbstractSourcePluginTestCase:

• SourceJarMojoTest → getSourceArchive(getTestTargetDir("project-005"), "project-005")
• TestSourceJarMojoTest → getTestSourceArchive(getTestTargetDir("project-005"), "project-005")

These are the same helpers the positive cases use via assertSourceArchive / assertTestSourceArchive, so each negative test now checks exactly the path its positive counterpart asserts, and the failure message names the file that was actually examined.

Testing

mvn test — 10 tests across both classes, all passing. Two lines changed, no production code touched.

• I hereby declare this contribution to be licenced under the Apache License Version 2.0, January 2004

[github-actions]

@elharo Please assign appropriate label to PR according to the type of change.