hardcode dockerhub username and ghcr.io repo for docker build

Currently, such a build most likely has access to secrets but
fails due to the wrong username logging with DockerHub when
rebase is done by anyone but @umputun.

.github/workflows/ci-build.yml

@@ -67,12 +67,12 @@ jobs:
           ref="$(echo ${GITHUB_REF} | cut -d'/' -f3)"
           echo "GITHUB_REF=${GITHUB_REF}, GITHUB_SHA=${GITHUB_SHA}, GIT_BRANCH=${ref}"
           echo ${GITHUB_PACKAGE_TOKEN} | docker login ghcr.io -u ${USERNAME} --password-stdin
-          echo ${DOCKER_HUB_TOKEN} | docker login -u ${USERNAME} --password-stdin
+          echo ${DOCKER_HUB_TOKEN} | docker login -u umputun --password-stdin
           docker buildx build --push \
               --build-arg SKIP_BACKEND_TEST=true --build-arg SKIP_FRONTEND_TEST=true --build-arg CI=github \
               --build-arg GITHUB_SHA=${GITHUB_SHA} --build-arg GIT_BRANCH=${ref} --build-arg GITHUB_REF=${GITHUB_REF} \
               --platform linux/amd64,linux/arm/v7,linux/arm64 \
-              -t ghcr.io/${USERNAME}/remark42:${ref} -t ${USERNAME}/remark42:${ref} .
+              -t ghcr.io/umputun/remark42:${ref} -t umputun/remark42:${ref} .
 
       - name: deploy tagged (latest) to ghcr.io and dockerhub
         if: ${{ startsWith(github.ref, 'refs/tags/') }}
@@ -86,7 +86,7 @@ jobs:
           ref="$(echo ${GITHUB_REF} | cut -d'/' -f3)"
           echo "GITHUB_REF=${GITHUB_REF}, GITHUB_SHA=${GITHUB_SHA}, GIT_BRANCH=${ref}"
           echo ${GITHUB_PACKAGE_TOKEN} | docker login ghcr.io -u ${USERNAME} --password-stdin
-          echo ${DOCKER_HUB_TOKEN} | docker login -u ${USERNAME} --password-stdin
+          echo ${DOCKER_HUB_TOKEN} | docker login -u umputun --password-stdin
           docker buildx build --push \
               --build-arg SKIP_BACKEND_TEST=true --build-arg SKIP_FRONTEND_TEST=true --build-arg CI=github \
               --build-arg GITHUB_SHA=${GITHUB_SHA} --build-arg GIT_BRANCH=${ref} --build-arg GITHUB_REF=${GITHUB_REF} \