Rename variable

Refs FerretDB#1657.

.github/RELEASE_CHECKLIST.md

@@ -26,10 +26,10 @@
 
 1. `task docker-cache`
 2. `task docker-push` with four tags (`X.Y.Z` without leading `v` and `latest` for both ghcr.io and Docker Hub):
-   * `task docker-push DOCKER_IMAGE=ferretdb/ferretdb:latest`
-   * `task docker-push DOCKER_IMAGE=ferretdb/ferretdb:<tag>`
-   * `task docker-push DOCKER_IMAGE=ghcr.io/ferretdb/ferretdb:latest`
-   * `task docker-push DOCKER_IMAGE=ghcr.io/ferretdb/ferretdb:<tag>`
+   * `task docker-push DOCKER_IMAGES=ferretdb/ferretdb:latest`
+   * `task docker-push DOCKER_IMAGES=ferretdb/ferretdb:<tag>`
+   * `task docker-push DOCKER_IMAGES=ghcr.io/ferretdb/ferretdb:latest`
+   * `task docker-push DOCKER_IMAGES=ghcr.io/ferretdb/ferretdb:<tag>`
    * Check <https://hub.docker.com/r/ferretdb/ferretdb/tags>, <https://github.com/FerretDB/FerretDB/pkgs/container/ferretdb>.
 
 ## Release

.github/workflows/docker.yml

@@ -115,7 +115,7 @@ jobs:
           password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Build Docker image ${{ steps.extract.outputs.ghcr }}
-        run: bin/task docker-push DOCKER_IMAGE=${{ steps.extract.outputs.ghcr }}
+        run: bin/task docker-push DOCKER_IMAGES=${{ steps.extract.outputs.ghcr }}
 
       - name: Check dirty
         run: |

Taskfile.yml

@@ -364,14 +364,14 @@ tasks:
   docker-push:
     deps: [gen-version]
     cmds:
-      - test {{.DOCKER_IMAGE}}
+      - test {{.DOCKER_IMAGES}}
       - >
         docker buildx build --builder=ferretdb
         --build-arg VERSION={{.VERSION}}
         --build-arg COMMIT={{.COMMIT}}
         --build-arg RACEFLAG={{.RACEFLAG}}
         --platform=linux/arm/v7,linux/arm64,linux/amd64
-        --tag={{.DOCKER_IMAGE}}
+        --tag={{.DOCKER_IMAGES}}
         --push .
     vars:
       VERSION: