Use GH_* instead of GITHUB_* for environment variables

According to [the docs], environment variables may not begin with
`GITHUB_`.

[the docs]: https://docs.github.com/en/free-pro-team@latest/actions/reference/environment-variables#naming-conventions-for-environment-variables

.github/workflows/ci.yml

@@ -151,8 +151,8 @@ jobs:
       - name: Deploy
         run: dart pub run grinder pkg-github-release pkg-github-linux
         env:
-          GITHUB_TOKEN: "${{ secrets.SASSBOT_GITHUB_TOKEN }}"
-          GITHUB_USER: sassbot
+          GH_TOKEN: "${{ secrets.GH_TOKEN }}"
+          GH_USER: sassbot
 
   deploy_github_macos:
     name: "Deploy Github: Mac OS"
@@ -167,8 +167,8 @@ jobs:
       - name: Deploy
         run: dart pub run grinder pkg-github-macos
         env:
-          GITHUB_TOKEN: "${{ secrets.SASSBOT_GITHUB_TOKEN }}"
-          GITHUB_USER: sassbot
+          GH_TOKEN: "${{ secrets.GH_TOKEN }}"
+          GH_USER: sassbot
 
   deploy_github_windows:
     name: "Deploy Github: Windows"
@@ -183,8 +183,8 @@ jobs:
       - name: Deploy
         run: dart pub run grinder pkg-github-windows
         env:
-          GITHUB_TOKEN: "${{ secrets.SASSBOT_GITHUB_TOKEN }}"
-          GITHUB_USER: sassbot
+          GH_TOKEN: "${{ secrets.GH_TOKEN }}"
+          GH_USER: sassbot
 
   deploy_npm:
     name: Deploy npm
@@ -247,8 +247,8 @@ jobs:
       - name: Deploy
         run: dart pub run grinder pkg-homebrew-update
         env:
-          GITHUB_TOKEN: "${{ secrets.SASSBOT_GITHUB_TOKEN }}"
-          GITHUB_USER: sassbot
+          GH_TOKEN: "${{ secrets.GH_TOKEN }}"
+          GH_USER: sassbot
 
   deploy_chocolatey:
     name: "Deploy Chocolatey"

tool/grind.dart

@@ -33,6 +33,8 @@ void main(List<String> args) {
           as Map<String, Object>;
   pkg.npmReadme.fn = () => _readAndResolveMarkdown("package/README.npm.md");
   pkg.standaloneName.value = "dart-sass";
+  pkg.githubUser.value = Platform.environment["GH_USER"];
+  pkg.githubPassword.value = Platform.environment["GH_TOKEN"];
 
   pkg.githubReleaseNotes.fn = () =>
       "To install Sass ${pkg.version}, download one of the packages below "