Update Github Markdown blockquotes snippets

[0237h]

The current snippets ghnote and ghwarn are using a deprecated syntax for rendering blockquotes information.

From the link above (update 14 Nov 2023):

The initial syntax using e.g. Note isn't supported any longer.

The new snippets format should be (e.g. for ghnote):

@@ -1,6 +1,5 @@
 <snippet>
-	<content><![CDATA[> **Note**
->
+	<content><![CDATA[> [!NOTE]
 > ${0:enter text}
 ]]></content>
 	<tabTrigger>ghnote</tabTrigger>
	<scope>text.html.markdown - meta.frontmatter - meta.disable-markdown - meta.code-fence - markup.raw</scope>
	<description>Markdown Admonition</description>
</snippet>

Additionally, support for ghtip, ghimportant and ghcaution can be added.

I can try to work on a PR based on the CONTRIBUTING.md guidelines when I have some time later.

[deathaxe]

I'll update them when integrating sublimehq/Packages#3892