fix(curriculum): grammatical issue in several challenges (freeCodeCamp#59723)

Co-authored-by: Dario-DC <105294544+Dario-DC@users.noreply.github.com>

Author: Drowsystudent

curriculum/challenges/english/21-a2-english-for-developers/learn-how-to-talk-about-updates-and-plans-for-tasks-and-projects/6614abad2657585c6229fb4a.md

@@ -96,7 +96,7 @@ Watch the video
       "startTime": 9.76,
       "finishTime": 12.68,
       "dialogue": {
-        "text": "It's cost effective and it will reach a broader audience.",
+        "text": "It's cost-effective and it will reach a broader audience.",
         "align": "center"
       }
     },

curriculum/challenges/english/21-a2-english-for-developers/learn-how-to-talk-about-updates-and-plans-for-tasks-and-projects/6614ad58c102e15df06c96d5.md

@@ -91,7 +91,7 @@ It implies targeting a wider or more diverse group of people.
       "startTime": 3.84,
       "finishTime": 6.76,
       "dialogue": {
-        "text": "It's cost effective and it will reach a broader audience.",
+        "text": "It's cost-effective and it will reach a broader audience.",
         "align": "center"
       }
     },

curriculum/challenges/english/21-a2-english-for-developers/learn-how-to-talk-about-updates-and-plans-for-tasks-and-projects/6614ae3e02cc465ebee68851.md

@@ -93,7 +93,7 @@ While `I think` shows Sophie's thought, it's the whole phrase `I think we're goi
       "startTime": 3.84,
       "finishTime": 6.76,
       "dialogue": {
-        "text": "It's cost effective and it will reach a broader audience.",
+        "text": "It's cost-effective and it will reach a broader audience.",
         "align": "center"
       }
     },

curriculum/challenges/english/21-a2-english-for-developers/learn-how-to-talk-about-updates-and-plans-for-tasks-and-projects/6614b1f8ee220c5f79df89b8.md

@@ -93,7 +93,7 @@ Ease of implementation isn't mentioned; her focus is on the strategy being cost-
       "startTime": 3.84,
       "finishTime": 6.76,
       "dialogue": {
-        "text": "It's cost effective and it will reach a broader audience.",
+        "text": "It's cost-effective and it will reach a broader audience.",
         "align": "center"
       }
     },

curriculum/challenges/english/21-a2-english-for-developers/learn-how-to-talk-about-updates-and-plans-for-tasks-and-projects/6614b3e52a6aca60bc3417fb.md

@@ -102,7 +102,7 @@ Brian's suggestion does not imply that he finds social media marketing ineffecti
       "startTime": 3.84,
       "finishTime": 6.76,
       "dialogue": {
-        "text": "It's cost effective and it will reach a broader audience.",
+        "text": "It's cost-effective and it will reach a broader audience.",
         "align": "center"
       }
     },

curriculum/challenges/english/24-b1-english-for-developers/learn-how-to-express-decisions-based-on-comparisons/67d57db13cd7aa1c85a6bae0.md

@@ -114,7 +114,7 @@ Watch the video.
       "startTime": 29.38,
       "finishTime": 35.4,
       "dialogue": {
-        "text": "That's true, but outsourcing might be more cost effective. It could save us time and resources.",
+        "text": "That's true, but outsourcing might be more cost-effective. It could save us time and resources.",
         "align": "left"
       }
     },

curriculum/challenges/english/24-b1-english-for-developers/learn-how-to-express-decisions-based-on-comparisons/67d78b42aaf0f93a96a8dae7.md

@@ -78,7 +78,7 @@ This means providing good results for the money spent. This is a compound word.
       "startTime": 1,
       "finishTime": 4.38,
       "dialogue": {
-        "text": "That's true, but outsourcing might be more cost effective.",
+        "text": "That's true, but outsourcing might be more cost-effective.",
         "align": "center"
       }
     },

curriculum/challenges/english/24-b1-english-for-developers/learn-how-to-express-decisions-based-on-comparisons/67d78eb913d0bd3d6e17f40a.md

@@ -90,7 +90,7 @@ He asks about `timelines`, meaning he is concerned with how long each option wil
       "startTime": 1,
       "finishTime": 4.38,
       "dialogue": {
-        "text": "That's true, but outsourcing might be more cost effective.",
+        "text": "That's true, but outsourcing might be more cost-effective.",
         "align": "center"
       }
     },