ci: deprecate travis in favour of GitHub actions

Travis has been b0rken for so long we might as well use the GitHub
actions for CI.

.github/workflows/test.yml

@@ -0,0 +1,63 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    continue-on-error: ${{ matrix.experimental }}
+    strategy:
+      matrix:
+        emacs_version:
+          - 24.1
+          - 24.5
+          - 25.1
+          - 25.3
+          - 26.1
+          - 26.3
+          - 27.1
+          - 27.2
+          - 28.1
+          - 28.2
+          - release-snapshot
+        experimental: false
+        include:
+          - emacs-version: snapshot
+            experimental: true
+          - emacs_version: 24.1
+            lint_ignore: 1
+    env:
+      EMACS_LINT_IGNORE: ${{ matrix.lint_ignore }}
+    steps:
+      - name: Install Emacs
+        uses: purcell/setup-emacs@master
+        with:
+          version: ${{ matrix.emacs_version }}
+
+      - name: Install Cask
+        run: curl -fsSL https://raw.githubusercontent.com/cask/cask/master/go | python
+
+      - name: Validate Cask
+        env:
+          PATH: "$HOME/.cask/bin:$PATH"
+        run: cask emacs --version
+
+      - name: Checkout Code
+        uses: actions/checkout@v3
+
+      - name: Install Elisp Deps
+        env:
+          PATH: "$HOME/.cask/bin:$PATH"
+        run: cask install
+
+      - name: Build
+        env:
+          PATH: "$HOME/.cask/bin:$PATH"
+        run: cask build
+
+      - name: Run ERT tests
+        env:
+          PATH: "$HOME/.cask/bin:$PATH"
+        run: cask exec ert-runner dired-rsync-ert.el