coverage only on master

Author: masci

Diff for: .drone.yml

@@ -16,12 +16,22 @@ steps:
     - task build
 
 - name: test
+  image: arduino/arduino-cli:drone-0.2.0
+  commands:
+    - task test
+    - task test-legacy
+
+# Contrary to other CI platforms, uploading reports to Codecov requires Drone to provide a token.
+# To avoid exposing the Codecov token to external PRs, we only upload coverage when we merge on
+# `master`.
+- name: coverage
   image: arduino/arduino-cli:drone-0.2.0
   environment:
     CODECOV_TOKEN:
       from_secret: codecov_token
   commands:
-    - task test
-    - task test-legacy
     - codecov -cF unit -f coverage_unit.txt -t $CODECOV_TOKEN
-    - codecov -cF integ -f coverage_integ.txt -t $CODECOV_TOKEN
+    - codecov -cF integ -f coverage_integ.txt -t $CODECOV_TOKEN
+  when:
+    branch:
+      - master