[jdk21u-dev] RFR: 8338595: Add more linesize for MIME decoder in macro bench test Base64Decode

[Goetz Lindenmaier]

I backport this for parity with 21.0.8-oracle.

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Commit messages:
 - Backport 7458952dedc0a34b5c7f3e9e228f9b18e08f19e3

Changes: https://git.openjdk.org/jdk21u-dev/pull/1420/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1420&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338595
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1420.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1420/head:pull/1420

PR: https://git.openjdk.org/jdk21u-dev/pull/1420