CFG: Reintroduce toString()s

ql/src/codeql_ruby/ast/Module.qll

@@ -213,7 +213,7 @@ class Module extends ModuleBase, ConstantWriteAccess, @module {
    * global scope, as in this example:
    *
    * ```rb
-   * class ::Foo
+   * module ::Foo
    * end
    * ```
    */

ql/src/codeql_ruby/ast/internal/Call.qll

@@ -53,9 +53,10 @@ module Call {
     final override Generated::Call generated;
 
     final override Expr getReceiver() {
-      if exists(generated.getReceiver())
-      then result = generated.getReceiver()
-      else result = generated.getMethod().(Generated::ScopeResolution).getScope()
+      result = generated.getReceiver()
+      or
+      not exists(generated.getReceiver()) and
+      result = generated.getMethod().(Generated::ScopeResolution).getScope()
     }
 
     final override string getMethodName() {