chore(actions): stop spamming stale notification for forks (#26578)

Closes `n/a`

Great project, but please stop spamming on stale notification for forks, thanks!

<img width="1374" alt="image" src="https://github.com/aws/aws-cdk/assets/984415/2581a5a9-6ebc-4b7a-91ce-48072997dda5">

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

Author: guessi

Diff for: .github/workflows/close-stale-issues.yml

@@ -8,6 +8,8 @@ on:
 
 jobs:
   cleanup:
+    # this workflow will always fail in forks; bail if this isn't running in the upstream
+    if: github.repository == 'aws/aws-cdk'
     permissions:
       issues: write
       contents: read

Diff for: .github/workflows/close-stale-prs.yml

@@ -5,6 +5,8 @@ on:
   workflow_dispatch:
 jobs:
   close-stale-prs:
+    # this workflow will always fail in forks; bail if this isn't running in the upstream
+    if: github.repository == 'aws/aws-cdk'
     permissions:
       pull-requests: write
     runs-on: ubuntu-latest

Diff for: .github/workflows/handle-stale-discussions.yml

@@ -7,6 +7,8 @@ on:
 
 jobs:
   handle-stale-discussions:
+    # this workflow will always fail in forks; bail if this isn't running in the upstream
+    if: github.repository == 'aws/aws-cdk'
     name: Handle stale discussions
     runs-on: ubuntu-latest
     permissions:
@@ -15,4 +17,4 @@ jobs:
       - name: Stale discussions action
         uses: aws-github-ops/handle-stale-discussions@v1
         env:
-          GITHUB_TOKEN:  ${{secrets.GITHUB_TOKEN}}
+          GITHUB_TOKEN:  ${{secrets.GITHUB_TOKEN}}