[jdk17] RFR: 8267271: Fix gc/arguments/TestNewRatioFlag.java expectedNewSize calculation

[Stefan Johansson]

Please review this test-fix to avoid failures on certain platforms.

**Summary**
Fixes an incorrect calculation in the test when trying to predict the new size given the `NewRatio`. The fix is not strictly bound to different platforms but to the resulting heap-size the test is run with. Both with Serial and Parallel the test fails if run on a platform using a heap alignment that forces the heap to be 104 MB instead of the specified 100 MB. It is a bit unclear why the test even passes with 100MB, since the calculation done in the test doesn't match the calculation done in the JVM. 

**Testing**
Manual testing to verify the fix actually fixes the issue and works with multiple page sizes. Mach5 testing on affected platforms to verify the fix is good there as well.

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Commit messages:
 - Fix gc/arguments/TestNewRatioFlag.java expectedNewSize calculation

Changes: https://git.openjdk.java.net/jdk17/pull/28/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17&pr=28&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267271
  Stats: 6 lines in 1 file changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk17/pull/28.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17 pull/28/head:pull/28

PR: https://git.openjdk.java.net/jdk17/pull/28