[lldb] Add packaging to testing requirements.txt

To fix CI after llvm#93712 landed.

Author: DavidSpickett

lldb/test/requirements.txt

@@ -4,3 +4,4 @@ psutil>=5.9.4
 # Pexpect tests are known not to work on Windows, so are disabled.
 # See llvm.org/pr22274.
 pexpect>=4.9.0; sys_platform != 'win32'
+packaging