add tags for scheduling the jobs on the docker runner

.gitlab-ci.yml

@@ -29,7 +29,8 @@ build-docker:
   only:
     changes:
       - Dockerfile
-
+  tags:
+    - docker
 
 build-binder:
   stage: build
@@ -44,7 +45,8 @@ build-binder:
     - ls
   only:
     - master
-
+  tags:
+    - docker
 
 test-docker:
   stage: test
@@ -55,7 +57,8 @@ test-docker:
   only:
     changes:
       - Dockerfile
-
+  tags:
+    - docker
 
 release-docker:
   stage: release
@@ -68,3 +71,5 @@ release-docker:
   only:
     changes:
       - Dockerfile
+  tags:
+    - docker
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