RFR: 8275512: Upgrade required version of jtreg to 6.1 [v2]

[Weijun Wang]

> As a follow up of JEP 411, we will soon disallow security manager by default. jtreg 6.1 does not set its own security manager if JDK version is >= 18.

Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:

  upgrade the version in GHA config
  
  only in patch2:
  unchanged:

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6012/files
  - new: https://git.openjdk.java.net/jdk/pull/6012/files/b86e799c..f5ffc49b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6012&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6012&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6012.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6012/head:pull/6012

PR: https://git.openjdk.java.net/jdk/pull/6012