fix(curriculum): Add new tests to check for space between result strings for two JavaScript challenges involving string concatenation (#46833)

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/concatenating-strings-with-plus-operator.md

@@ -32,6 +32,12 @@ Build `myStr` from the strings `This is the start.` and `This is the end.` using
 
 # --hints--
 
+`myStr` should have a single space character between the two strings.
+
+```js
+assert(/start\. This/.test(myStr));
+```
+
 `myStr` should have a value of the string `This is the start. This is the end.`
 
 ```js

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/concatenating-strings-with-the-plus-equals-operator.md

@@ -28,6 +28,12 @@ Build `myStr` over several lines by concatenating these two strings: `This is th
 
 # --hints--
 
+`myStr` should have a single space character between the two strings.
+
+```js
+assert(/sentence\. This/.test(myStr));
+```
+
 `myStr` should have a value of the string `This is the first sentence. This is the second sentence.`
 
 ```js