Bump actions/upload-artifact from 3 to 4 (#13780)

Update `upload-artifact` from v3 to v4 to avoid the failure of `External
Server Tests` (I encountered this error when opening
[#13779](https://github.com/redis/redis/pull/13779)):

> Error: This request has been automatically failed because it uses a
deprecated version of `actions/upload-artifact: v3`. Learn more:
https://github.blog/changelog/2024-04-16-deprecation-notice-v3-of-the-artifact-actions/

.github/workflows/external.yml

@@ -26,7 +26,7 @@ jobs:
             --tags -slow
     - name: Archive redis log
       if: ${{ failure() }}
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       with:
         name: test-external-redis-log
         path: external-redis.log
@@ -53,7 +53,7 @@ jobs:
             --tags -slow
     - name: Archive redis log
       if: ${{ failure() }}
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       with:
         name: test-external-cluster-log
         path: external-redis.log
@@ -76,7 +76,7 @@ jobs:
             --tags "-slow -needs:debug"
       - name: Archive redis log
         if: ${{ failure() }}
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: test-external-redis-log
           path: external-redis.log