Fix docs for plugin install via proxy on Windows

This commit addresses an issue with the docs for plugin install via a
proxy on Windows where the HTTP proxy options were incorrectly
specified.

Relates #23757

docs/plugins/plugin-script.asciidoc

@@ -187,8 +187,8 @@ Or on Windows:
 
 [source,shell]
 ------------------------------------
-set ES_JAVA_OPTS="-DproxyHost=host_name -DproxyPort=port_number -Dhttps.proxyHost=host_name -Dhttps.proxyPort=https_port_number"
-bin/elasticsearch-plugin install analysis-icu
+set ES_JAVA_OPTS="-Dhttp.proxyHost=host_name -Dhttp.proxyPort=port_number -Dhttps.proxyHost=host_name -Dhttps.proxyPort=https_port_number"
+bin\elasticsearch-plugin install analysis-icu
 ------------------------------------
 
 === Plugins directory