chore(psalm): forbid iconv

iconv transliteration is locale- and config-dependent; use
UnicodeString::ascii() from symfony/string instead.

Assisted-by: Claude:claude-sonnet-4-6
Signed-off-by: Christoph Wurst <1374172+ChristophWurst@users.noreply.github.com>

Author: ChristophWurst

psalm.xml

@@ -130,6 +130,9 @@
 		<file name="build/stubs/php-polyfill.php" />
 		<file name="build/stubs/oca_talk_share_helper_shareapicontroller.php" />
 	</stubs>
+	<forbiddenFunctions>
+		<function name="iconv"/>
+	</forbiddenFunctions>
 	<issueHandlers>
 		<LessSpecificReturnStatement errorLevel="error"/>
 		<LessSpecificReturnType errorLevel="error"/>