[CI] Resolve "SBA mono detector test cases (stv and ltv) are missing"

• Related issues: #1365
• Requested reviewers: @tyagiri @kiene

Reason why this change is needed

• One code path was not covered by the SBA mono test vector.

Description of the change

• Modify the test vector to have some signal parts with all channels but W exactly equal to zero.

Affected operating points

• No codec change