tests(build.yml): add experimental for snapshots

Author: jcs090218

.github/workflows/build.yml

@@ -11,11 +11,23 @@ on:
 jobs:
   build:
     runs-on: ${{ matrix.os }}
+    continue-on-error: ${{ matrix.experimental }}
     strategy:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        emacs-version: [26.1, 26.2, 26.3, 27.1, 27.2, 28.1, snapshot]
+        emacs-version: [26.1, 26.2, 26.3, 27.1, 27.2, 28.1]
+        experimental: [false]
+        include:
+        - os: ubuntu-latest
+          emacs-version: snapshot
+          experimental: true
+        - os: macos-latest
+          emacs-version: snapshot
+          experimental: true
+        - os: windows-latest
+          emacs-version: snapshot
+          experimental: true
 
     steps:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it