RFR: 8345220: Serial: Refactor TenuredGeneration::promotion_attempt_is_safe

[Albert Mingkun Yang]

Trivial using MIN2 to replace `>=` and `||` for better readability.

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Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/22444/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22444&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345220
  Stats: 6 lines in 1 file changed: 3 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/22444.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22444/head:pull/22444

PR: https://git.openjdk.org/jdk/pull/22444