Messed up static and instance overloads

[ap32]

Describe the bug

Version: 15.1.0

Messed up static and instance overloads

To Reproduce

// MRE.ts

class MRE {
  foo(): number;
  foo(n: number): number;
  foo(n = 1): number {
    return n;
  }

  static foo(): number;
  static foo(n: number): number;
  static foo(n = 1): number {
    return n;
  }
}

import { Project } from "ts-morph";
const project = new Project();
project.addSourceFilesAtPaths(path.resolve(__dirname, "./MRE.ts"));

const source = project.getSourceFileOrThrow(
  path.resolve(__dirname, "./MRE.ts")
);

const MRE = source.getClassOrThrow("MRE");

for (const method of MRE.getMethods()) {
  if (method.isOverload()) continue;
  console.log(
    `${
      method.isStatic() ? "static" : "instance"
    } method "${method.getName()}" has "${
      method.getOverloads().length
    }" overloads.`
  );
}

const result = project.createSourceFile(
  path.resolve(__dirname, "./result.ts")
);

result.addClass(MRE.getStructure());
result.saveSync();
process.exit(0);

Expected behavior

instance method "foo" has 2 overloads.
static method "foo" has 2 overloads.

class MRE {
    foo(): number;
    foo(n: number): number;
    foo(n = 1): number {
        return n;
    }

    static foo(): number;
    static foo(n: number): number;
    static foo(n = 1): number {
        return n;
    }
}

Actual behavior

instance method "foo" has 4 overloads.
static method "foo" has 4 overloads.

class MRE {
    foo(): number;
    foo(n: number): number;
    static foo(): number;
    static foo(n: number): number;
    foo(n = 1): number {
        return n;
    }

    foo(): number;
    foo(n: number): number;
    static foo(): number;
    static foo(n: number): number;
    static foo(n = 1): number {
        return n;
    }
}