RFR: 8329527: Opcode.IFNONNULL.primaryTypeKind() is not ReferenceType

[Adam Sotona]

`Opcode.IFNONNULL.primaryTypeKind()` wrongly returned `IntType` instead of the right `ReferenceType`.
Primary type kinds of `BRANCH` opcodes have yet no functional effect in the Class-File API.
This simple patch fixes the typo.

Please review.

Thank you,
Adam

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Commit messages:
 - 8329527: Opcode.IFNONNULL.primaryTypeKind() is not ReferenceType

Changes: https://git.openjdk.org/jdk/pull/18593/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18593&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329527
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18593.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18593/head:pull/18593

PR: https://git.openjdk.org/jdk/pull/18593
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