ci: add a job to run tests on forks

Author: machow

.github/workflows/ci.yml

@@ -16,6 +16,7 @@ jobs:
   tests:
     name: "Tests"
     runs-on: ${{ matrix.os }}
+    if: ${{ !github.event.pull_request.head.repo.fork }}
     strategy:
       fail-fast: false
       matrix:
@@ -60,6 +61,7 @@ jobs:
   test-rsconnect:
     name: "Test RSConnect"
     runs-on: ubuntu-latest
+    if: ${{ !github.event.pull_request.head.repo.fork }}
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
@@ -83,6 +85,27 @@ jobs:
         run: |
           pytest pins -m 'fs_rsc and not skip_on_github'
 
+
+  test-fork:
+    name: "Test a fork PR (no secrets)"
+    runs-on: ubuntu-latest
+    if: ${{ github.event.pull_request.head.repo.fork }}
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.10
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+
+          python -m pip install -e .[test]
+      - name: Run tests
+        run: |
+          # TODO: better way to disable all cloud backend tests?
+          pytest pins -m 'not fs_rsc and not fs_s3 and not skip_on_github'
+
+
   check-cross-compatibility:
     name: "Check cross lib compatibility"
     runs-on: ubuntu-latest