Prepare for rename default branch to main (#5)

.github/workflows/ci.yml

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e67ec6e..85e142e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -2,9 +2,9 @@
 
 on:
   push:
-    branches: ['master']
+    branches: ['master', 'main']
   pull_request:
-    branches: ['master']
+    branches: ['master', 'main']
 
 jobs:
   lint:
@@ -37,4 +37,4 @@
       - name: Run pytest
         run: |
           pip install -r test-requirements.txt
-          pytest airflow_client/test
\ No newline at end of file
+          pytest airflow_client/test