Add CategoryToTag regression test for nested category classes

[timtebeek]

Adds a regression test for CategoryToTag covering a @Category referencing a nested class, e.g. @Category(Appenders.Cassandra.class).

• This is the exact scenario reported in Issue discovered on log4j-cassandra/src/test/java/org/apache/logging/log4j/cassandra/CassandraAppenderIT.java with Change type #447, where the recipe threw ClassCastException: J$FieldAccess cannot be cast to J$Identifier. The root cause was assuming category.getTarget() was always a simple J.Identifier, which is not the case for Outer.Inner.class references.

• The underlying bug was already fixed in a692563 (CategoryToTag: Support qualified class names, which added the convertToTagName helper to handle J.FieldAccess targets). However, the existing tests only cover package-qualified names (foo.FastTests.class); none covered the nested-class scenario from Issue discovered on log4j-cassandra/src/test/java/org/apache/logging/log4j/cassandra/CassandraAppenderIT.java with Change type #447. This test locks in that behavior so the issue can be closed.

• Fixes Issue discovered on log4j-cassandra/src/test/java/org/apache/logging/log4j/cassandra/CassandraAppenderIT.java with Change type #447

[timtebeek]

Closing without merging — #447 was already fixed on main (see a692563). This was a verification-only regression test; the bug no longer reproduces, so closing both the issue and this PR.