Use master of js-sdk when running CI on master

We previously checked out develop js-sdk even when building / testing
mster. This would have worked usually, except when we have non-backwards
compat changes on the js-sdk which we sometimes do with unstable
interfaces (like sliding sync).

This changes to use the master branch.

.github/workflows/static_analysis.yaml

@@ -15,6 +15,8 @@ env:
     # These must be set for fetchdep.sh to get the right branch
     REPOSITORY: ${{ github.repository }}
     PR_NUMBER: ${{ github.event.pull_request.number }}
+    # If run on the master branch, we need to fetch matching branches
+    DEFAULT_BRANCH: ${{ github.ref == 'refs/heads/master' && 'master' || '' }}
 
 permissions: {} # No permissions required
 
@@ -31,7 +33,8 @@ jobs:
                   node-version: "lts/*"
 
             - name: Install Dependencies
-              run: "./scripts/layered.sh"
+              run: |
+                  ./scripts/layered.sh "$DEFAULT_BRANCH"
 
             - name: Typecheck
               run: "yarn run lint:types"