Use v2 of GitHub Actions where available (GH-20232)

Automerge-Triggered-By: @Mariatta
(cherry picked from commit 7fbe65d)

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

.github/workflows/build_msi.yml

@@ -21,14 +21,14 @@ jobs:
     name: 'Windows (x86) Installer'
     runs-on: windows-latest
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Build CPython installer
       run: .\Tools\msi\build.bat -x86
 
   build_win_amd64:
     name: 'Windows (x64) Installer'
     runs-on: windows-latest
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Build CPython installer
       run: .\Tools\msi\build.bat -x64

.github/workflows/coverage.yml

@@ -25,7 +25,7 @@ jobs:
     env:
       OPENSSL_VER: 1.1.1f
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Install Dependencies
       run: sudo ./.github/workflows/posix-deps-apt.sh
     - name: 'Restore OpenSSL build'
@@ -73,7 +73,7 @@ jobs:
     name: 'Ubuntu (C Coverage)'
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Install Dependencies
       run: sudo ./.github/workflows/posix-deps-apt.sh
     - name: Configure CPython

.github/workflows/doc.yml

@@ -22,7 +22,7 @@ jobs:
     name: 'Docs'
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: 'Install Dependencies'
       run: sudo ./.github/workflows/posix-deps-apt.sh && sudo apt-get install wamerican
     - name: 'Configure CPython'