Move coverage step to common workflow for PRs and pushes to main (#984)

So we can consistently collect coverage data on the default branch, which CodeCov needs
to compare branch coverage and line data against.

.github/workflows/ci.yml

@@ -91,20 +91,3 @@ jobs:
         with:
           command: fmt
           args: --all -- --check
-
-  coverage:
-    name: Coverage
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/toolchain@v1
-        with:
-          toolchain: stable
-          override: true
-      - name: Run cargo-tarpaulin
-        uses: actions-rs/tarpaulin@v0.1
-        with:
-          version: 'latest'
-          timeout: 600
-      - name: Upload coverage report to Codecov
-        uses: codecov/codecov-action@v1.0.13

.github/workflows/coverage.yml

@@ -0,0 +1,28 @@
+name: CI
+
+on:
+  pull_request:
+    branches:
+      - main
+  push:
+    branches:
+      - main
+
+jobs:
+
+  coverage:
+    name: Coverage
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+      - name: Run cargo-tarpaulin
+        uses: actions-rs/tarpaulin@v0.1
+        with:
+          version: 'latest'
+          timeout: 600
+      - name: Upload coverage report to Codecov
+        uses: codecov/codecov-action@v1.0.13