Bump action versions.

Bump actions/checkout to v4.
Bump docker/setup-qemu-action to v3.
Bump docker/setup-buildx-action to v3.

.github/workflows/build.yml

@@ -16,7 +16,7 @@ jobs:
       latest_version: "2.54.1"
       download_url: "https://github.com/pgbackrest/pgbackrest/archive/release"
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
 
     - name: Get repo tag
       if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags/v')
@@ -25,14 +25,16 @@ jobs:
         echo ::set-output name=repo_tag::$(echo ${GITHUB_REF} | cut -d'/' -f3)
     
     - name: Set up QEMU
-      uses: docker/setup-qemu-action@v1
+      uses: docker/setup-qemu-action@v3
 
     - name: Set up Docker Buildx
       id: buildx
-      uses: docker/setup-buildx-action@v1
+      uses: docker/setup-buildx-action@v3
 
     - name: Available platforms
-      run: echo ${{ steps.buildx.outputs.platforms }}
+      run: echo ${BUILDX_PLATFORMS}
+      env:
+        BUILDX_PLATFORMS: ${{ steps.buildx.outputs.platforms }}
 
     - name: Build pgbackrest image
       run: |
@@ -155,7 +157,7 @@ jobs:
     env: 
       download_url: "https://github.com/arenadata/pgbackrest/archive"
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
 
     - name: Get repo tag
       if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags/v')
@@ -164,14 +166,16 @@ jobs:
         echo ::set-output name=repo_tag::$(echo ${GITHUB_REF} | cut -d'/' -f3)
     
     - name: Set up QEMU
-      uses: docker/setup-qemu-action@v1
+      uses: docker/setup-qemu-action@v3
 
     - name: Set up Docker Buildx
       id: buildx
-      uses: docker/setup-buildx-action@v1
+      uses: docker/setup-buildx-action@v3
 
     - name: Available platforms
-      run: echo ${{ steps.buildx.outputs.platforms }}
+      run: echo ${BUILDX_PLATFORMS}
+      env:
+        BUILDX_PLATFORMS: ${{ steps.buildx.outputs.platforms }}
 
     - name: Build pgbackrest gpdb image
       run: |