docs: fix formatting of PULL_REQUEST_TEMPLATE.md (#26512)

This change enables developers to check the checkboxes or update them
after they submitted a PR.

PR Close #26512

.github/PULL_REQUEST_TEMPLATE.md

@@ -10,17 +10,17 @@ Please check if your PR fulfills the following requirements:
 What kind of change does this PR introduce?
 
 <!-- Please check the one that applies to this PR using "x". -->
-```
-[ ] Bugfix
-[ ] Feature
-[ ] Code style update (formatting, local variables)
-[ ] Refactoring (no functional changes, no api changes)
-[ ] Build related changes
-[ ] CI related changes
-[ ] Documentation content changes
-[ ] angular.io application / infrastructure changes
-[ ] Other... Please describe:
-```
+
+- [ ] Bugfix
+- [ ] Feature
+- [ ] Code style update (formatting, local variables)
+- [ ] Refactoring (no functional changes, no api changes)
+- [ ] Build related changes
+- [ ] CI related changes
+- [ ] Documentation content changes
+- [ ] angular.io application / infrastructure changes
+- [ ] Other... Please describe:
+
 
 ## What is the current behavior?
 <!-- Please describe the current behavior that you are modifying, or link to a relevant issue. -->
@@ -32,10 +32,10 @@ Issue Number: N/A
 
 
 ## Does this PR introduce a breaking change?
-```
-[ ] Yes
-[ ] No
-```
+
+- [ ] Yes
+- [ ] No
+
 
 <!-- If this PR contains a breaking change, please describe the impact and migration path for existing applications below. -->