bug #26590 Make sure form errors is valid HTML (Nyholm)

This PR was merged into the 3.4 branch.

Discussion
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Make sure form errors is valid HTML

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #26461
| License       | MIT
| Doc PR        |

Using `<div>` and `<ul>` in a `<label>` is not valid HTML. This PR uses `<span>`s instead and some Bootstrap 4 classes to make it look just like before.

Commits
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5dcaaadb5e Make sure form errors is valid HTML

Author: fabpot

Resources/views/Form/bootstrap_4_layout.html.twig

@@ -267,12 +267,12 @@
 
 {% block form_errors -%}
     {%- if errors|length > 0 -%}
-        <div class="{% if form is not rootform %}invalid-feedback d-block{% else %}alert alert-danger{% endif %}">
-            <ul class="list-unstyled mb-0">
-                {%- for error in errors -%}
-                    <li><span class="initialism form-error-icon badge badge-danger">{{ 'Error'|trans({}, 'validators') }}</span> <span class="form-error-message">{{ error.message }}</span></li>
-                {%- endfor -%}
-            </ul>
-        </div>
+        <span class="{% if form is not rootform %}invalid-feedback d-block{% else %}alert alert-danger{% endif %}">
+            {%- for error in errors -%}
+                <span class="mb-0 d-block">
+                    <span class="initialism form-error-icon badge badge-danger">{{ 'Error'|trans({}, 'validators') }}</span> <span class="form-error-message">{{ error.message }}</span>
+                </span>
+            {%- endfor -%}
+        </span>
     {%- endif %}
 {%- endblock form_errors %}