Integrated: 8377443: G1: Remove unnecessary cast in ResizeTLABAndSwapCardTableTask

[Thomas Schatzl]

Hi all,

  please review this trivial removal of an unnecessary cast because `tlab()` is a member of `Thread` already and does not need `JavaThread`.

Testing: local compilation, gha

Thanks,
  Thomas

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Commit messages:
 - 8377443

Changes: https://git.openjdk.org/jdk/pull/29628/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29628&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377443
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/29628.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29628/head:pull/29628

PR: https://git.openjdk.org/jdk/pull/29628