SI-8523 Adjust test for namespace interpolation

This test fails after we try to fix SI-8523 in the compiler.
But the test is actually at fault here, as it was relying on
the loose matching performed by the compiler's SymbolXMLBuilder.

The fix for SI-8523 that triggered the failure:

   https://github.com/scala/scala/commit/8d175b907

The original commit that introduced this test:

   https://github.com/scala/scala/commit/e1ffc05b10be6

Review by @som-snytt