feat: Update pull_request_template.md (#6302)

Update pull_request_template.md

add notes about testing mobile layouts to the test plan prompts

.github/pull_request_template.md

@@ -7,9 +7,9 @@ _[Summary of change, motivation, and context.]_
 - _Note: Your PR title must follow conventions [outlined here](https://github.com/Uniswap/interface#contributions)._
 
 ## Screen Capture
-| Before           | After           |
-| ---------------- |-----------------|
-|  _insert_before_ | _insert_after_  |
+| Before           | After (Desktop)  | After (Mobile) |
+| ---------------- |----------------- | -------------- |
+|  _insert_before_ | _insert_after_   | _insert_after_ |
 
 
 ## Test Plan
@@ -17,6 +17,8 @@ _[Summary of change, motivation, and context.]_
 
 _[Steps of how you are testing the change and ensuring no regression.]_
 
+_[Different devices and screen sizes that may be affected and how you tested.]_
+
 #### Automated
 - [ ] Unit test
 - [ ] Integration/E2E test