chore: add condition to prioritization workflows (#33150)

### Issue # (if applicable)

N/A

### Reason for this change

The prioritization workflows should not run in forks.

### Description of changes

Added a condition to when the workflows should run.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: samson-keung

.github/workflows/project-prioritization-assignment.yml

@@ -1,7 +1,7 @@
 name: PR Prioritization
 on:
   pull_request_target:
-    types: 
+    types:
       - labeled
       - opened
       - reopened
@@ -10,6 +10,7 @@ on:
 
 jobs:
   prioritize:
+    if: github.repository == 'aws/aws-cdk'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4

.github/workflows/project-prioritization-r2-assignment.yml

@@ -6,10 +6,11 @@ on:
 
 jobs:
   update_project_status:
+    if: github.repository == 'aws/aws-cdk'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      
+
       - name: Check and assign R2 Priority to PRs
         uses: actions/github-script@v7
         with:

.github/workflows/project-prioritization-r5-assignment.yml

@@ -6,6 +6,7 @@ on:
 
 jobs:
   update_project_status:
+    if: github.repository == 'aws/aws-cdk'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4