fix(ci): bind deploy PR API to secrets.CI_GITEA_TOKEN (CAR-1195)

deploy-dev and deploy-uat had CI_GITEA_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
which is the package-scoped container-registry token. PR creation and
auto-merge against cartsnitch/infra would 403 on the first real push.
Bind to secrets.CI_GITEA_TOKEN (the token the infra checkout already
uses for branch push) so the Gitea API calls have repo-write scope.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.gitea/workflows/ci.yml

@@ -544,7 +544,7 @@ jobs:
 
       - name: Commit and push to infra (via PR)
         env:
-          CI_GITEA_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+          CI_GITEA_TOKEN: ${{ secrets.CI_GITEA_TOKEN }}
         run: |
           cd infra
           git config user.name "cartsnitch-ci[bot]"
@@ -670,7 +670,7 @@ jobs:
 
       - name: Commit and push to infra (via PR)
         env:
-          CI_GITEA_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+          CI_GITEA_TOKEN: ${{ secrets.CI_GITEA_TOKEN }}
         run: |
           cd infra
           git config user.name "cartsnitch-ci[bot]"