Update workflows to main branch

.github/workflows/gem-build.yml

@@ -2,7 +2,7 @@ name: Build Ruby Gem
 
 on:
   pull_request:
-    branches: [ master ]
+    branches: [ main ]
 
 jobs:
   test:

.github/workflows/jekyll-build.yml

@@ -2,9 +2,9 @@ name: Jekyll Build
 
 on:
   push:
-    branches: [ master ]
+    branches: [ main ]
   pull_request:
-    branches: [ master ]
+    branches: [ main ]
 
 jobs:
   build:

.github/workflows/workflow-test.yml

@@ -3,7 +3,7 @@ name: Workflow Test
 on:
   workflow_run:
     workflows: ["Jekyll build"]
-    branches: ["master"]
+    branches: ["main"]
     types:
       - completed