TST: Add RC testing workflow

[ci skip]

.github/workflows/predeps_workflow.yml

@@ -0,0 +1,36 @@
+name: rc-testing
+
+on:
+  workflow_dispatch:
+
+# Cancel duplicate builds
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  tests:
+    runs-on: ${{ matrix.os }}
+    needs: initial_check
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v3
+      with:
+        fetch-depth: 0
+    - name: Set up Python
+      uses: actions/setup-python@v4
+      with:
+        python-version: '3.11'
+    - name: Install and build
+      run: |
+        python -m pip install --upgrade pip setuptools wheel
+        python -m pip install numpy scipy astropy ginga --pre
+        python -m pip install -e .[test]
+    - name: Test
+      run: pytest