[jdk8u-dev] RFR: 8056283: @ignore tools/javac/defaultMethods/Assertions.java until JDK-8047675 is fixed

[SendaoYan]

Hi all,

I want to backport [JDK-8047675](https://bugs.openjdk.org/browse/JDK-8047675) to jdk8u-dev, but I found that this PR is the prefixed PR to backport [JDK-8047675](https://bugs.openjdk.org/browse/JDK-8047675) to jdk8u-dev.

This PR only add `@ignore` derictive to disable the test. Test-fix only, no risk.

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Commit messages:
 - Backport d66c4567eea47bd74037b49acbd85d71a2cf239a

Changes: https://git.openjdk.org/jdk8u-dev/pull/669/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=669&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8056283
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/669.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev.git pull/669/head:pull/669

PR: https://git.openjdk.org/jdk8u-dev/pull/669