RFR: 8279547: [vectorapi] Enable vector cast tests after JDK-8278948

[Quan Anh Mai]

Hi,

This patch enables 2 vector cast operations that fail before.

Thank you very much.

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Commit messages:
 - enable tests

Changes: https://git.openjdk.java.net/jdk/pull/6976/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6976&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279547
  Stats: 5 lines in 1 file changed: 0 ins; 1 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6976.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6976/head:pull/6976

PR: https://git.openjdk.java.net/jdk/pull/6976