chore: Rename master branch to main branch

Author: sorairolake

.github/workflows/CI.yaml

@@ -9,7 +9,7 @@ on:
   push:
     branches:
       - "develop"
-      - "master"
+      - "main"
   schedule:
     - cron: "0 0 * * 0"
 

.github/workflows/REUSE.yaml

@@ -9,7 +9,7 @@ on:
   push:
     branches:
       - "develop"
-      - "master"
+      - "main"
 
 jobs:
   reuse:

CONTRIBUTING.adoc

@@ -24,7 +24,7 @@ Please see the {commit-messages-guide-url}[Commit messages guide] and the
 == Submitting a pull request
 
 . Create a working branch from the `develop` branch. The branch name should be
-  something other than `develop` or `master`.
+  something other than `develop` or `main`.
 . Create your patch. If your change is a feature or a bugfix, please add a test
   case if possible. Note that the change must pass the CI.
 . Please update the copyright information if possible. This project is