Swap failing CircleCI status for passing GH Action

I'm ambivalent about Circle vs. Actions, but the former is failing
missing a key in order to clone the repo, and I think I lack access to
fix that. Since it's only a simple workflow, seemed easiest to recreate
in Actions - and as that passes (as of
d62f1625be) it seems to make more sense to
use that for a nice green status than red from Circle.

.github/workflows/main.yml

@@ -14,3 +14,8 @@ jobs:
 
       - name: Compile
         run: make
+
+      - uses: actions/upload-artifact@v2
+        with:
+          name: examples
+          path: examples/*.pdf