fix(curriculum): improve tests in markdown converter lab (freeCodeCamp#61899)

Author: Dario-DC

curriculum/challenges/english/25-front-end-development/lab-markdown-to-html-converter/66f55eac933ff64ce654ca74.md

@@ -134,6 +134,7 @@ const testDiv = document.createElement("div");
 testDiv.innerHTML = convertMarkdown();
 const testH1 = testDiv.querySelector("h1")
 assert.notExists(testH1);
+assert.equal(testDiv.innerText, input.value)
 ```
 
 When the value of `#markdown-input` is `# title 1` followed by `# alternate title` on a new line, `convertMarkdown()` should return `<h1>title 1</h1><h1>alternate title</h1>`.
@@ -202,6 +203,7 @@ const testDiv = document.createElement("div");
 testDiv.innerHTML = convertMarkdown();
 const testH2 = testDiv.querySelector("h2")
 assert.notExists(testH2);
+assert.equal(testDiv.innerText, input.value)
 ```
 
 When the value of `#markdown-input` is `## title 2` followed by `## title 2 alt` on a new line, `convertMarkdown()` should return `<h2>title 2</h2><h2>title 2 alt</h2>`.
@@ -270,6 +272,7 @@ const testDiv = document.createElement("div");
 testDiv.innerHTML = convertMarkdown();
 const testH3 = testDiv.querySelector("h3")
 assert.notExists(testH3);
+assert.equal(testDiv.innerText, input.value)
 ```
 
 When the value of `#markdown-input` is `### title 3` followed by `### third title` on a new line, `convertMarkdown()` should return `<h3>title 3</h3><h3>third title</h3>`.
@@ -779,6 +782,7 @@ const testDiv = document.createElement("div");
 testDiv.innerHTML = convertMarkdown();
 const testQuote = testDiv.querySelector("blockquote")
 assert.notExists(testQuote);
+assert.equal(testDiv.innerText, input.value)
 ```
 
 When the value of `#markdown-input` is `> **this is a *quote***`, `convertMarkdown()` should return `<blockquote><strong>this is a <em>quote</em></strong></blockquote>`.