CI: Do not save the ccache for PRs (8.3+)

see GH-14168

.github/workflows/nightly.yml

@@ -801,6 +801,7 @@ jobs:
         with:
           key: "${{github.job}}-${{hashFiles('php/main/php_version.h')}}"
           append-timestamp: false
+          save: ${{ github.event_name != 'pull_request' }}
       - name: build PHP
         run: |
           cd php

.github/workflows/push.yml

@@ -225,6 +225,7 @@ jobs:
         with:
           key: "${{github.job}}-${{hashFiles('main/php_version.h')}}"
           append-timestamp: false
+          save: ${{ github.event_name != 'pull_request' }}
       - name: ./configure
         run: |
           set -x