Add check for HTML in translations (#35615)

* Add check for HTML in translations

and remove existing html

* Add test

homeassistant/helpers/config_validation.py

@@ -465,6 +465,15 @@ def string(value: Any) -> str:
     return str(value)
 
 
+def string_with_no_html(value: Any) -> str:
+    """Validate that the value is a string without HTML."""
+    value = string(value)
+    regex = re.compile(r"<[a-z][\s\S]*>")
+    if regex.search(value):
+        raise vol.Invalid("the string should not contain HTML")
+    return str(value)
+
+
 def temperature_unit(value: Any) -> str:
     """Validate and transform temperature unit."""
     value = str(value).upper()