RFR: 8372294: Fix Malformed problem list entry in ProblemList-jvmti-stress-agent.txt

[Chris Plummer]

ProblemList-jvmti-stress-agent.txt fails to pass verification because it uses a tab character instead of spaces. 

I'd like to push this as a trivial change.

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Commit messages:
 - get rid of tab char

Changes: https://git.openjdk.org/jdk/pull/28441/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28441&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372294
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/28441.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28441/head:pull/28441

PR: https://git.openjdk.org/jdk/pull/28441