Add code snippet with 2 consecutive new lines

This demonstrates the issue that https://github.com/11ty/eleventy-plugin-syntaxhighlight/pull/5 fixes, and could serve as kind of a regression test for the fix. :)

posts/firstpost.md

@@ -19,4 +19,7 @@ function myCommand() {
 	let counter = 0;
 	counter++;
 }
+
+// Test with a line break above this line.
+console.log('Test');
 ```

posts/thirdpost.md

@@ -13,6 +13,9 @@ function myCommand() {
 	let counter = 0;
 	counter++;
 }
+
+// Test with a line break above this line.
+console.log('Test');
 ```
 
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