Update sync-from-upstream.yml GH action from 'master' to 'main' (#925)

* Update sync-from-upstream.yml

Change 'master' to 'main' as default for GH action since new default branch name is 'main'

* Update .github/workflows/sync-from-upstream.yml

---------

Co-authored-by: Evan Gibler <evan.gibler@panther.com>

.github/workflows/sync-from-upstream.yml

@@ -7,7 +7,7 @@ on:
   workflow_dispatch: # or on button click  
 
 env:
-  YOUR_REPO_PRIMARY_BRANCH_NAME: "master"
+  YOUR_REPO_PRIMARY_BRANCH_NAME: "main"
 
 jobs:
   check_upstream:
@@ -104,4 +104,3 @@ jobs:
         run: |
           echo "unhandled exception in PR create step. Check output of that step."
           exit 128
-