Pre-existing gopls issues should not be reported as regressions

-- p.go --
package p

func F() {
	x := 42
}

-- .commit --
Initial commit with existing gopls issue

-- p.go --
package p

func F() {
	x := 42
	// unrelated change
}

-- .commit --
Make a change but keep the same gopls issue

-- .run_test --
OK