Upgrade to typed: true with let(false, Boolean)

IMHO this is a design bug in Ruby copied into Sorbet.
A Boolean class should exist in Ruby, or Sorbet should infer it,
without us having to declare it with T.let

Without this:

```
./library/packages/src/modules/PackageKit.rb:52: Changing the type of a variable in a loop is not permitted https://srb.help/7001
    52 |        ret = true if Builtins.regexpmatch(line, "boolean.*true")
                      ^^^^
  Existing variable has type: FalseClass
  Attempting to change type to: TrueClass
```

library/packages/src/modules/PackageKit.rb

@@ -1,4 +1,4 @@
-# typed: false
+# typed: true
 # ***************************************************************************
 #
 # Copyright (c) 2002 - 2012 Novell, Inc.
@@ -29,6 +29,7 @@
 #
 # This is a wrrapper around PackageKit DBus interface.
 require "yast"
+require "sorbet-runtime"
 
 module Yast
   class PackageKitClass < Module
@@ -43,7 +44,7 @@ def IsRunning
 
       out = Convert.to_map(SCR.Execute(path(".target.bash_output"), cmd))
 
-      ret = false
+      ret = T.let(false, T::Boolean)
       lines = Builtins.splitstring(Ops.get_string(out, "stdout", ""), "\n")
 
       Builtins.foreach(lines) do |line|