ci: resolve gitian automation failures on dashevo repo (#5267)

## Issue being fixed or feature implemented
Automation in private dashevo GitHub was failing due to the branch
trying to be built not having the automation be the newer tagged based
system. as such, if you simply tag a commit from the dashpay repo and
try to build it using automation, the build would fail. This should
resolve the issue. Recommended to BP so that we don't have this issue
when building v19.x branch builds

## What was done?


## How Has This Been Tested?
Creating a docker image should now be as simple pushing a branch and tag
to dashevo/dash; start the automation on branch develop with tag
previously specified

## Breaking Changes


## Checklist:
- [x] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have added or updated relevant unit/integration/functional/e2e
tests
- [ ] I have made corresponding changes to the documentation

**For repository code-owners and collaborators only**
- [x] I have assigned this pull request to a milestone

contrib/containers/deploy/Dockerfile.GitHubActions.Gitian

@@ -5,7 +5,7 @@ LABEL description="Dockerised DashCore"
 
 ARG USER_ID
 ARG GROUP_ID
-ARG BRANCH
+ARG TAG
 
 ENV HOME /home/dash
 
@@ -23,7 +23,7 @@ RUN apt-get update && \
     ca-certificates \
     && rm -rf /var/lib/apt/lists/*
 
-COPY dashcore-binaries/${BRANCH}/dashcore* /home/dash
+COPY dashcore-binaries/${TAG}/dashcore* /home/dash
 
 RUN mach=$(uname -m) \
       && case $mach in aarch64) arch="aarch64-linux-gnu"; ;; x86_64) arch="x86_64-linux-gnu"; ;;  *) echo "ERROR: Machine type $mach not supported."; ;; esac \