Fix dialyzer warning in Code.format_string!/2

Tentative fix for #14927

Author: sabiwara

lib/elixir/lib/code.ex

@@ -1090,7 +1090,7 @@ defmodule Code do
   @doc since: "1.6.0"
   @spec format_string!(binary, [format_opt]) :: iodata
   def format_string!(string, opts \\ []) when is_binary(string) and is_list(opts) do
-    line_length = Keyword.get(opts, :line_length, 98)
+    {line_length, opts} = Keyword.pop(opts, :line_length, 98)
 
     to_quoted_opts =
       [

lib/elixir/test/elixir/fixtures/dialyzer/regressions.ex

@@ -0,0 +1,10 @@
+defmodule Dialyzer.Regressions do
+  def format_opts do
+    Code.format_string!("",
+      line_length: 120,
+      force_do_end_blocks: true,
+      locals_without_parens: true,
+      migrate: true
+    )
+  end
+end

lib/elixir/test/elixir/kernel/dialyzer_test.exs

@@ -185,6 +185,11 @@ defmodule Kernel.DialyzerTest do
     assert_dialyze_no_warnings!(context)
   end
 
+  test "no warning in various non-regression cases", context do
+    copy_beam!(context, Dialyzer.Regressions)
+    assert_dialyze_no_warnings!(context)
+  end
+
   defp copy_beam!(context, module) do
     name = "#{module}.beam"
     File.cp!(Path.join(context.base_dir, name), Path.join(context.outdir, name))