RFR: 8307620: [IR Framework] Readme mentions JTREG_WHITE_LIST_FLAGS instead of JTREG_WHITELIST_FLAGS

[Eric Nothum]

README now refers to JTREG_WHITELIST_FLAGS instead of JTREG_WHITE_LIST_FLAGS

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Commit messages:
 - 8307620: Update README.md

Changes: https://git.openjdk.org/jdk/pull/14377/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14377&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307620
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14377.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14377/head:pull/14377

PR: https://git.openjdk.org/jdk/pull/14377