Update slackapi/slack-github-action action to v2

Author: renovate[bot]

.github/workflows/build-image.yml

@@ -140,7 +140,7 @@ jobs:
 
       - name: Notify on newly built image
         if: ${{ inputs.push_image }}
-        uses: slackapi/slack-github-action@v1.18.0
+        uses: slackapi/slack-github-action@v2.1.1
         env:
           SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
           SLACK_WEBHOOK_TYPE: INCOMING_WEBHOOK

.github/workflows/build-pixi-image.yml

@@ -136,7 +136,7 @@ jobs:
 
       - name: Notify on newly built image
         if: ${{ inputs.push_image }}
-        uses: slackapi/slack-github-action@v1.18.0
+        uses: slackapi/slack-github-action@v2.1.1
         env:
           SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
           SLACK_WEBHOOK_TYPE: INCOMING_WEBHOOK