Speed up Zip64SizeTest with a larger buffer size

It reduces the runtime by ~30%. It takes ~21 seconds on
the emulator

Bug: 227925195
Test: atest CtsLibcoreOjTestCases:test.java.util.zip.ZipFile.Zip64SizeTest#validateZipEntrySizes
Change-Id: Ifc4bd0bc372c0bec528230a077a49199ac8524f3
1 file changed