Rename Replay speed to Game speed in Singleplayer (#1145)

## Description:

Change the title of the replay panel from "Replay speed" to "Game speed"
when in a Singleplayer game.

BEFORE

![afbeelding](https://github.com/user-attachments/assets/1ff17f05-ebae-4adf-a90d-618a87ca7432)

AFTER
![Game
speed](https://github.com/user-attachments/assets/5af78157-17e9-4e00-b4c3-d36c33b026f9)

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

tryout33

resources/lang/en.json

@@ -446,7 +446,8 @@
     "alliances": "Alliances"
   },
   "replay_panel": {
-    "replay_speed": "Replay speed"
+    "replay_speed": "Replay speed",
+    "game_speed": "Game speed"
   },
   "error_modal": {
     "crashed": "Game crashed!",