[jdk21] RFR: 8311645: Memory leak in jspawnhelper spawnChild after JDK-8307990

[Aleksey Shipilev]

Clean backport. Fixes the regression introduced in JDK 21.

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Commit messages:
 - Backport 401c3dea5d8823bc9c0f40506ddad46e983ebf68

Changes: https://git.openjdk.org/jdk21/pull/120/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21&pr=120&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311645
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21/pull/120.diff
  Fetch: git fetch https://git.openjdk.org/jdk21.git pull/120/head:pull/120

PR: https://git.openjdk.org/jdk21/pull/120