Engine: <%= -%> does not trim trailing newline (#1361)

### Description

The `-%>` trim modifier on `<%= %>` (expression) tags does not suppress
the trailing newline. Standard ERB trims the trailing newline when `-%>`
is used, but Herb preserves it.

### Reproduction

Template:

```erb
hello<%= -%>
world
```

Expected output (standard ERB):

`helloworld`

Actual output (Herb):

```
hello
world
```

### Notes

<% -%> (statement tags) trim correctly — the issue is specific to <%=
-%> (expression tags). This is a common Rails idiom for controlling
whitespace in email and other templates.

Author: joelhawksley

lib/herb/engine/compiler.rb

@@ -372,7 +372,7 @@ def process_erb_tag(node, skip_comment_check: false)
         code = node.content.value.strip
 
         if erb_output?(opening)
-          process_erb_output(opening, code)
+          process_erb_output(node, opening, code)
         else
           apply_trim(node, code)
         end
@@ -487,9 +487,11 @@ def find_token_before_code_sequence(tokens, whitespace_index)
         search_index >= 0 ? tokens[search_index] : nil
       end
 
-      def process_erb_output(opening, code)
+      def process_erb_output(node, opening, code)
+        has_right_trim = node.tag_closing&.value == "-%>"
         should_escape = should_escape_output?(opening)
         add_expression_with_escaping(code, should_escape)
+        @trim_next_whitespace = true if has_right_trim
       end
 
       def should_escape_output?(opening)

sig/herb/engine/compiler.rbs

@@ -148,5 +148,26 @@ class WhitespaceTrimmingTest < Minitest::Spec
       assert_compiled_snapshot(template)
       assert_evaluated_snapshot(template, enforce_erubi_equality: true)
     end
+
+    test "expression tag with right trim removes following newline" do
+      template = "<%= \"hello\" -%>\nworld"
+
+      assert_compiled_snapshot(template)
+      assert_evaluated_snapshot(template, enforce_erubi_equality: true)
+    end
+
+    test "expression tag with right trim inline" do
+      template = "<%= \"hello\" -%> world"
+
+      assert_compiled_snapshot(template)
+      assert_evaluated_snapshot(template, enforce_erubi_equality: true)
+    end
+
+    test "expression tag with right trim as no-op for newline control" do
+      template = "2024-07-09 with the filters: \"archived:false\"<%= -%>.\n"
+
+      assert_compiled_snapshot(template)
+      assert_evaluated_snapshot(template, enforce_erubi_equality: true)
+    end
   end
 end