RFR: 8376398: [TESTBUG] Testing of Unsafe native (re)allocation is sensitive to current JDK native memory use

[Eirik Bjørsnøs]

Please consider this PR which bumps the size of attempted allocations with 1m such that the tests are less brittle to  JDK-internal native memory use.

These tests currently run with `XX:MallocLimit=other:100m:oom`, but also try to allocate `100 * 1024 * 1024` bytes.

With current JDK-internal native memory use, these allocation fail with OOM. When the JDK itself uses less memory, these tests start failing because allocation succeeds.

I think we should simply try to allocate one more megabyte than the configured limit, which should cause the allocation to fail regardless of internal JVM native memory use.

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Commit messages:
 - Attempt to allocate 1m more than limit

Changes: https://git.openjdk.org/jdk/pull/29429/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29429&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8376398
  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/29429.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29429/head:pull/29429

PR: https://git.openjdk.org/jdk/pull/29429