[jdk21u] RFR: 8309663: test fails "assert(check_alignment(result)) failed: address not aligned: 0x00000008baadbabe"

[Aleksey Shipilev]

Clean backport to fix a corner case in JVMTI + concurrent GCs.

Additional testing:
 - [x] macos-aarch64-server-fastdebug, `jdk_loom hotspot_loom`
 - [ ] linux-x86_64-server-fastdebug, `tier1 tier2 tier3`
 - [ ] linux-x86_64-server-fastdebug, `tier1 tier2 tier3` with `-XX:+UseShenandoahGC`

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Commit messages:
 - Backport 83edffa608d998a118d1d12f62d73be40a8982bc

Changes: https://git.openjdk.org/jdk21u/pull/253/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=253&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309663
  Stats: 5 lines in 2 files changed: 3 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u/pull/253.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/253/head:pull/253

PR: https://git.openjdk.org/jdk21u/pull/253