[java] StringToString doesn't trigger on string literals

[ghost]

Affects PMD Version:6.41.0

Rule:StringToString

Please provide the rule name and a link to the rule documentation:
https://pmd.github.io/latest/pmd_rules_java_performance.html#stringtostring

Description:
I found a false negative about the rule StringToString, please refer to the minimized sample below.

PMD should have reported a warning at line 3, but it does not. However, this is definitely a String object calls toString() method. So, I think this is a false negative.

Code Sample demonstrating the issue:

class Impl {
  String foo() {
    return "123".toString();
  }
}

Expected outcome:

PMD should report a violation at line 3, but doesn't. This is a false-negative.

Running PMD through: [Maven]