build across supported oses

Author: rotu

.github/workflows/main.yml

@@ -4,12 +4,10 @@ jobs:
     strategy:
       matrix:
         ros-distro: [eloquent]
-    runs-on: ubuntu-latest
-    # NB: this line would break if we tried to make ros-distro
-    #     an environment variable instead of a matrix entry
+        runs-on: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{matrix.runs-on}}
     container: ros:${{matrix.ros-distro}}-ros-base
     steps:
-      - run: sudo rm -rf /etc/ros/rosdep/
       - uses: ros-tooling/setup-ros@0.0.25
         with:
           required-ros-distributions: ${{matrix.ros-distro}}