MLE-23607 : Node Client Sparql test fails for 12-nightly on Jenkins

[anu3990]

No description provided.

[Copilot]

Pull Request Overview

This PR fixes a failing Node Client SPARQL test for server version 12-nightly by updating the logic that extracts the default graph path from the query explanation output. The test was failing due to changes in the structure of the explanation output between different server versions.

• Consolidates version-specific conditional logic for handling different server explanation output formats
• Simplifies the test assertion by extracting the default graph value into a single variable

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