ci: migrate to Github Actions Concurrency for cancelling workflows (googleapis#1158)

Replaces `styfle/cancel-workflow-action` with [Github Actions concurrency](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#concurrency). When the workflow has `cancel-in-progress: true`, this will cancel any currently running job or workflow in the same concurrency group which should be the same behaviour as `styfle/cancel-workflow-action`.

Closes googleapis#1151

Author: parthea

.github/workflows/tests.yaml

@@ -9,14 +9,14 @@ on:
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch:
 
+concurrency:
+  group: tests-${{ github.head_ref }}
+  cancel-in-progress: true
+
 jobs:
   docs:
     runs-on: ubuntu-latest
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          access_token: ${{ github.token }}
       - uses: actions/checkout@v2
       - name: Set up Python 3.8
         uses: actions/setup-python@v2
@@ -30,10 +30,6 @@ jobs:
   mypy:
     runs-on: ubuntu-latest
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          access_token: ${{ github.token }}
       - uses: actions/checkout@v2
       - name: Set up Python 3.8
         uses: actions/setup-python@v2
@@ -50,10 +46,6 @@ jobs:
         target: [showcase, showcase_alternative_templates]
     runs-on: ubuntu-latest
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          access_token: ${{ github.token }}
       - uses: actions/checkout@v2
       - name: Set up Python 3.8
         uses: actions/setup-python@v2
@@ -93,10 +85,6 @@ jobs:
         target: [showcase_mtls, showcase_mtls_alternative_templates]
     runs-on: ubuntu-latest
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          access_token: ${{ github.token }}
       - uses: actions/checkout@v2
       - name: Setup temp directory
         run: |
@@ -156,10 +144,6 @@ jobs:
             variant: _alternative_templates
     runs-on: ubuntu-latest
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          access_token: ${{ github.token }}
       - uses: actions/checkout@v2
       - name: Set up Python ${{ matrix.python }}
         uses: actions/setup-python@v2
@@ -187,10 +171,6 @@ jobs:
   showcase-unit-add-iam-methods:
     runs-on: ubuntu-latest
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          access_token: ${{ github.token }}
       - uses: actions/checkout@v2
       - name: Set up Python 3.8
         uses: actions/setup-python@v2
@@ -221,10 +201,6 @@ jobs:
       matrix:
         variant: ['', _alternative_templates]
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          access_token: ${{ github.token }}
       - uses: actions/checkout@v2
       - name: Set up Python 3.8
         uses: actions/setup-python@v2
@@ -252,10 +228,6 @@ jobs:
   snippetgen:
     runs-on: ubuntu-latest
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          access_token: ${{ github.token }}
       - uses: actions/checkout@v2
       - name: Set up Python 3.8
         uses: actions/setup-python@v2
@@ -276,10 +248,6 @@ jobs:
         python: [3.6, 3.7, 3.8, 3.9]
     runs-on: ubuntu-latest
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          access_token: ${{ github.token }}
       - uses: actions/checkout@v2
       - name: Set up Python ${{ matrix.python }}
         uses: actions/setup-python@v2
@@ -305,10 +273,6 @@ jobs:
             variant: _alternative_templates
     runs-on: ubuntu-latest
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          access_token: ${{ github.token }}
       - uses: actions/checkout@v2
       - name: Set up Python ${{ matrix.python }}
         uses: actions/setup-python@v2
@@ -328,10 +292,6 @@ jobs:
     runs-on: ubuntu-latest
     container: gcr.io/gapic-images/googleapis
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          access_token: ${{ github.token }}
       - uses: actions/checkout@v2
       - name: Cache Bazel files
         id: cache-bazel
@@ -359,10 +319,6 @@ jobs:
   style-check:
     runs-on: ubuntu-latest
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          access_token: ${{ github.token }}
       - uses: actions/checkout@v2
       - name: Set up Python 3.8
         uses: actions/setup-python@v2