Fix AtAjLTWTests::testLTWDumpProxy for Java 16

Fix AtAjLTWTests::testLTWDumpProxy for Java 16

Before Java 16, JDK proxies were given a virtual package name of
'com.sun.proxy'. Now the packages are numbered 'jdk.proxy[n]', i.e.
'jdk.proxy1', 'jdk.proxy2' etc. This makes the package-name-derived path
name here less predictable. In our simple runtime scenario, we can be
pretty sure than the counter starts at 1 because it is the first and
only proxy we create.

TODO: A better solution would be a recursive filtered search via
Files.walk, ideally added as a recursive search option for
CountingFilenameFilter.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>