Warn safe_level and later args even without -w

because, when Ruby 3.1 is released, Ruby 2.5, the last version with the
old method signature, will have been EOL. Therefore we can safely warn
the old interface from Ruby 3.1.

lib/erb.rb

@@ -809,14 +809,14 @@ class ERB
   def initialize(str, safe_level=NOT_GIVEN, legacy_trim_mode=NOT_GIVEN, legacy_eoutvar=NOT_GIVEN, trim_mode: nil, eoutvar: '_erbout')
     # Complex initializer for $SAFE deprecation at [Feature #14256]. Use keyword arguments to pass trim_mode or eoutvar.
     if safe_level != NOT_GIVEN
-      warn 'Passing safe_level with the 2nd argument of ERB.new is deprecated. Do not use it, and specify other arguments as keyword arguments.', uplevel: 1 if $VERBOSE || !ZERO_SAFE_LEVELS.include?(safe_level)
+      warn 'Passing safe_level with the 2nd argument of ERB.new is deprecated. Do not use it, and specify other arguments as keyword arguments.', uplevel: 1
     end
     if legacy_trim_mode != NOT_GIVEN
-      warn 'Passing trim_mode with the 3rd argument of ERB.new is deprecated. Use keyword argument like ERB.new(str, trim_mode: ...) instead.', uplevel: 1 if $VERBOSE
+      warn 'Passing trim_mode with the 3rd argument of ERB.new is deprecated. Use keyword argument like ERB.new(str, trim_mode: ...) instead.', uplevel: 1
       trim_mode = legacy_trim_mode
     end
     if legacy_eoutvar != NOT_GIVEN
-      warn 'Passing eoutvar with the 4th argument of ERB.new is deprecated. Use keyword argument like ERB.new(str, eoutvar: ...) instead.', uplevel: 1 if $VERBOSE
+      warn 'Passing eoutvar with the 4th argument of ERB.new is deprecated. Use keyword argument like ERB.new(str, eoutvar: ...) instead.', uplevel: 1
       eoutvar = legacy_eoutvar
     end
 
@@ -829,8 +829,6 @@ def initialize(str, safe_level=NOT_GIVEN, legacy_trim_mode=NOT_GIVEN, legacy_eou
   end
   NOT_GIVEN = Object.new
   private_constant :NOT_GIVEN
-  ZERO_SAFE_LEVELS = [0, nil]
-  private_constant :ZERO_SAFE_LEVELS
 
   ##
   # Creates a new compiler for ERB.  See ERB::Compiler.new for details

test/erb/test_erb.rb

@@ -663,26 +663,20 @@ def test_half_working_comment_backward_compatibility
 
   # [deprecated] These interfaces will be removed later
   def test_deprecated_interface_warnings
-    [nil, 0].each do |safe|
-      assert_warning(/2nd argument of ERB.new is deprecated/) do
-        ERB.new('', safe)
-      end
-    end
-
-    [1, 2].each do |safe|
+    [nil, 0, 1, 2].each do |safe|
       assert_warn(/2nd argument of ERB.new is deprecated/) do
         ERB.new('', safe)
       end
     end
 
     [nil, '', '%', '%<>'].each do |trim|
-      assert_warning(/3rd argument of ERB.new is deprecated/) do
+      assert_warn(/3rd argument of ERB.new is deprecated/) do
         ERB.new('', nil, trim)
       end
     end
 
     [nil, '_erbout', '_hamlout'].each do |eoutvar|
-      assert_warning(/4th argument of ERB.new is deprecated/) do
+      assert_warn(/4th argument of ERB.new is deprecated/) do
         ERB.new('', nil, nil, eoutvar)
       end
     end