cleanup github actions config

- cancel previous workflow runs
- limit actions to changes on master branch
- update actions/cache config
- only upload code coverage status once

Author: willnorris

.github/workflows/tests.yml

@@ -1,29 +1,48 @@
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
 name: tests
 
 jobs:
   test:
     strategy:
       matrix:
-        go-version: [1.x, 1.14.x]
+        go-version: [1.x, 1.15.x]
         platform: [ubuntu-latest]
+        include:
+          # only update test coverage stats with most recent go version on linux
+          - go-version: 1.x
+            platform: ubuntu-latest
+            update-coverage: true
     runs-on: ${{ matrix.platform }}
 
     steps:
+    - name: Cancel previous workflow runs
+      uses: styfle/cancel-workflow-action@0.8.0
+      with:
+        access_token: ${{ github.token }}
+
+    - uses: actions/checkout@v2
     - uses: actions/setup-go@v2
       with:
         go-version: ${{ matrix.go-version }}
-    - uses: actions/checkout@v2
+    - run: go version
 
     - name: Cache go modules
       uses: actions/cache@v2
       with:
         path: ~/go/pkg/mod
-        key: ${{ runner.os }}-go-${{ hashFiles('go.sum') }}
+        key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
         restore-keys: ${{ runner.os }}-go-
 
     - name: Run go test
       run: go test -v -race -coverprofile coverage.txt -covermode atomic ./...
 
     - name: Upload coverage to Codecov
+      if: ${{ matrix.update-coverage }}
       uses: codecov/codecov-action@v1