goheader: fix invalid position

[ldez]

Location() returns the position of the first element that needs to be changed, and Expected contains all the header lines.

If the first element to change is at L3 and the beginning of the header is at L1, you have a beautiful Christmas tree based on comment separators.

The problem has been here since the introduction of the auto fix for goheader (golangci-lint v1.57.0).

https://github.com/golangci/golangci-lint/pull/4396/files#diff-36750bd1c0da16befa607266d41aca09351630ed97e4ae48f96b63f60e6cbb6dR103

To reproduce

/*
Copyright 2024 The Awesome Project Authors

Use of this source code is governed by LICENSE
*/
package sandbox

func Foo() {}

linters:
  disable-all: true
  enable:
    - goheader

linters-settings:
  goheader:
    values:
      const:
        AUTHOR: The Awesome Project Authors
    template: |-
        Copyright 2024 {{ AUTHOR }}
  
        Use of this source code is governed by LICENSE.md

Then run golangci-lint run --fix

---

Also now it displays the right position of the problem.

Before:

$ golangci-lint run                                                
main.go:3:47: Missed string: .md (goheader)

Use of this source code is governed by LICENSE
*/

package sandbox
$ 

After:

$ ./golangci-lint run
main.go:4:47: Missed string: .md (goheader)
Use of this source code is governed by LICENSE
                                              ^
$