CI: less redundancy, push coverage (#448)

Right now PRs from non-fork branches run twice on each platform.
This eliminates the redundancy.

Also push coverage.

Author: timholy

.github/workflows/CI.yml

@@ -1,7 +1,10 @@
 name: CI
 on:
-  - push
-  - pull_request
+  pull_request:
+  push:
+    branches:
+      - master
+    tags: '*'
 jobs:
   test:
     name: Julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.arch }} - ${{ github.event_name }}
@@ -40,4 +43,8 @@ jobs:
             ${{ runner.os }}-test-
             ${{ runner.os }}-
       - uses: julia-actions/julia-buildpkg@v1
-      - uses: julia-actions/julia-runtest@v1
+      - uses: julia-actions/julia-runtest@v1
+      - uses: julia-actions/julia-processcoverage@v1
+      - uses: codecov/codecov-action@v1
+        with:
+          file: lcov.info