Fix yaml spec link

Author: Loenix

components/yaml/yaml_format.rst

@@ -335,4 +335,4 @@ The following YAML features are not supported by the Symfony Yaml component:
 
 .. _`ISO-8601`: https://www.iso.org/iso-8601-date-and-time-format.html
 .. _`YAML website`: https://yaml.org/
-.. _`YAML specification`: https://www.yaml.org/spec/1.2/spec.html
+.. _`YAML specification`: https://yaml.org/spec/1.2/spec.html