Only update documentation for gbdev/rgbds

Prevent the relevant GitHub Actions from running on forks

.github/workflows/create-release-docs.yml

@@ -6,6 +6,7 @@ on:
 
 jobs:
   build:
+    if: github.repository_owner == 'gbdev'
     runs-on: ubuntu-18.04
     steps:
       - name: Checkout rgbds@release

.github/workflows/update-master-docs.yml

@@ -17,6 +17,7 @@ on:
 
 jobs:
   build:
+    if: github.repository_owner == 'gbdev'
     runs-on: ubuntu-18.04
     steps:
       - name: Checkout rgbds@master