[foreign-jextract] RFR: Fix NativeScope

[Maurizio Cimadamore]

The recent merge has broken the generated `NativeScope` class. The fix is trivial.

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Commit messages:
 - Fix NativeScope

Changes: https://git.openjdk.java.net/panama-foreign/pull/518/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=518&range=00
  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/518.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/518/head:pull/518

PR: https://git.openjdk.java.net/panama-foreign/pull/518