Update GitHub Actions to use upload/download artifact v4 API

* Updated `actions/download-artifact` to `v4` in `bitbake-build`
  and `podman-robot` workflows. Adjusted inputs to include
  `pattern` and `merge-multiple`.
* Updated `actions/upload-artifact` to `v4` in `bitbake-repo` workflow.

See:

* https://github.blog/changelog/2024-04-16-deprecation-notice-v3-of-the-artifact-actions/
* https://github.blog/news-insights/product-news/get-started-with-v4-of-github-actions-artifacts/
* https://github.com/actions/upload-artifact/blob/main/docs/MIGRATION.md

Author: psaavedra

.github/actions/bitbake-build/action.yml

@@ -27,9 +27,10 @@ runs:
         echo "RELEASE=${{ inputs.repo_release }}"
         echo "======================================================================"
     - name: Download timestamp artifact
-      uses: actions/download-artifact@v3
+      uses: actions/download-artifact@v4
       with:
-        name: timestamp.txt
+        pattern: timestamp.txt
+        merge-multiple: true
     - name: Get timestamp prefix
       id: timestamp
       shell: bash

.github/actions/bitbake-repo/action.yml

@@ -42,7 +42,7 @@ runs:
         git rebase tmp/main
         popd
     - name: Upload timestamp prefix artifact
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       with:
         name: timestamp.txt
         path: timestamp.txt

.github/actions/podman-robot/action.yml

@@ -27,9 +27,10 @@ runs:
         echo "RELEASE=${{ inputs.repo_release }}"
         echo "======================================================================"
     - name: Download timestamp artifact
-      uses: actions/download-artifact@v3
+      uses: actions/download-artifact@v4
       with:
-        name: timestamp.txt
+        pattern: timestamp.txt
+        merge-multiple: true
     - name: Get timestamped prefix
       id: timestamp
       shell: bash