stdlib: the headers keyword for CSV.foreach can take String

The headers keyword option of `CSV.foreach` can take String, Symbol and
Array too.  Therefore, this adds them to the type definition.

refs:
* https://docs.ruby-lang.org/en/3.3/CSV.html#method-c-foreach
* https://docs.ruby-lang.org/en/3.3/CSV.html#class-CSV-label-Options+for+Parsing

Note:

In https://github.com/ruby/rbs/pull/1738/files#r1468802569, @m11o
was aware of the lackness of the types, but they determined to support
only "true" value at first.

Author: tk0miya

stdlib/csv/0/csv.rbs

@@ -1722,8 +1722,8 @@ class CSV < Object
   #     would read `UTF-32BE` data from the file but transcode it to `UTF-8`
   #     before parsing.
   #
-  def self.foreach: (String | IO path, ?String mode, headers: true, **untyped options) { (::CSV::Row arg0) -> void } -> void
-                  | (String | IO path, ?String mode, headers: true, **untyped options) -> Enumerator[::CSV::Row, void]
+  def self.foreach: (String | IO path, ?String mode, headers: true | :first_row | Array[untyped] | String, **untyped options) { (::CSV::Row arg0) -> void } -> void
+                  | (String | IO path, ?String mode, headers: true | :first_row | Array[untyped] | String, **untyped options) -> Enumerator[::CSV::Row, void]
                   | (String | IO path, ?String mode, **untyped options) { (::Array[String?] arg0) -> void } -> void
                   | (String | IO path, ?String mode, **untyped options) -> Enumerator[::Array[String?], void]
 

test/stdlib/CSV_test.rb

@@ -27,11 +27,23 @@ def test_foreach
                      CSV, :foreach, path, headers: false, &string_array_block
     assert_send_type "(IO path, headers: bool) { (CSV::Row) -> void } -> void",
                      CSV, :foreach, File.open(path), headers: true, &csv_row_array_block
+    assert_send_type "(String path, headers: :first_row) { (CSV::Row) -> void } -> void",
+                     CSV, :foreach, path, headers: :first_row, &csv_row_array_block
+    assert_send_type "(String path, headers: Array[untyped]) { (CSV::Row) -> void } -> void",
+                     CSV, :foreach, path, headers: ["name"], &csv_row_array_block
+    assert_send_type "(String path, headers: String) { (CSV::Row) -> void } -> void",
+                     CSV, :foreach, path, headers: "name", &csv_row_array_block
 
     assert_send_type "(String path, **untyped) -> Enumerator[Array[String?], void]",
                      CSV, :foreach, path, encoding: 'UTF-8'
     assert_send_type "(String path, headers: bool) -> Enumerator[CSV::Row, void]",
                      CSV, :foreach, path, headers: true
+    assert_send_type "(String path, headers: :first_row) -> Enumerator[CSV::Row, void]",
+                     CSV, :foreach, path, headers: :first_row
+    assert_send_type "(String path, headers: Array[untyped]) -> Enumerator[CSV::Row, void]",
+                     CSV, :foreach, path, headers: ["name"]
+    assert_send_type "(String path, headers: String) -> Enumerator[CSV::Row, void]",
+                     CSV, :foreach, path, headers: "name"
     assert_send_type "(String path, headers: bool, **untyped) -> Enumerator[CSV::Row, void]",
                      CSV, :foreach, path, headers: true, encoding: 'UTF-8'
   end