Changed quotation marks to Spanish ones (#5968)

As stated by the Royal Spanish Academy in "Ortografía de la lengua española" (2010 edition, page 386), spanish quotation marks (« ») should be used instead of the english ones (“ ”).
This can also can be checked online in https://www.rae.es/dpd/comillas.

We, unfortunately, don't have a style guide to go by here, but this seems more plausible

Co-authored-by: ruben2s <ruben2s@users.noreply.github.com>
Co-authored-by: Sebastian Karcher <karcher@u.northwestern.edu>

spanish-legal.csl

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<style xmlns="http://purl.org/net/xbiblio/csl" class="note" default-locale="es-ES" version="1.0" demote-non-dropping-particle="sort-only">
+<style xmlns="http://purl.org/net/xbiblio/csl" class="note" version="1.0" demote-non-dropping-particle="sort-only" default-locale="es-ES">
   <info>
     <title>Spanish Legal (Español)</title>
     <id>http://www.zotero.org/styles/spanish-legal</id>
@@ -111,7 +111,7 @@
         <text variable="title" text-case="capitalize-first" font-style="italic"/>
       </if>
       <else>
-        <text variable="title" text-case="capitalize-first" prefix="“" suffix="”"/>
+        <text variable="title" text-case="capitalize-first" quotes="true"/>
       </else>
     </choose>
   </macro>
@@ -121,7 +121,7 @@
         <text variable="title" text-case="capitalize-first" font-style="italic" suffix=", cit." form="short"/>
       </if>
       <else>
-        <text variable="title" text-case="capitalize-first" prefix="“" suffix="”, cit." form="short"/>
+        <text variable="title" text-case="capitalize-first" quotes="true" suffix=", cit." form="short"/>
       </else>
     </choose>
   </macro>