GA: remove merging with upstream branch

According to
actions/checkout#15 (comment), GA
when triggered by a pull request will check out the merged state of the
repo.

Also therefore no need to clone to depth greater than 1.

.github/workflows/test.yml

@@ -39,16 +39,8 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v2
         with:
-          fetch-depth: 0
           submodules: true
 
-      - name: Merge with master
-        run: |
-          git config --global user.email "[email protected]"
-          git config --global user.name "SkyPortal CI"
-          git merge origin/master
-          git submodule update
-
       - name: Write SkyPortal configs
         run: |
           cat << EOF > config.yaml