Only run "update" job from scheduled pipelines

Stop attempting to unconditionally mirror the tor repository in GitLab
CI.  This prevented developers from enabling GitLab CI on master
because the "update" job would attempt to run, causing an unuseful CI
failure.  Fixes bug 23755.

.gitlab-ci.yml

@@ -10,6 +10,8 @@ build:
     - "make install"
 
 update:
+  only:
+    - schedules
   script: 
     - "apt-get install -y --fix-missing git openssh-client"
     
@@ -36,4 +38,4 @@ update:
     - "mkdir tor"
     - "cd tor" 
     - git clone --bare https://git.torproject.org/tor.git
-    - git push --mirror git@oniongit.eu:network/tor.git
+    - git push --mirror git@oniongit.eu:network/tor.git

changes/bug23755

@@ -0,0 +1,4 @@
+  o Minor bugfixes (testing):
+    - Stop unconditionally mirroring the tor repository in GitLab CI.
+      This prevented developers from enabling GitLab CI on master.
+      Fixes bug 23755; bugfix on 0.3.2.2-alpha.