bpo-40548: Github Actions: update actions/checkout to v2 (GH-20164)

Signed-off-by: Filipe Laíns <lains@archlinux.org>
(cherry picked from commit c444108)

Co-authored-by: Filipe Laíns <lains@archlinux.org>

Author: miss-islington

.github/workflows/build.yml

@@ -33,7 +33,7 @@ jobs:
     needs: check_source
     if: needs.check_source.outputs.run_tests == 'true'
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Build CPython
       run: .\PCbuild\build.bat -e -p Win32
     - name: Display build info
@@ -47,7 +47,7 @@ jobs:
     needs: check_source
     if: needs.check_source.outputs.run_tests == 'true'
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Build CPython
       run: .\PCbuild\build.bat -e -p x64
     - name: Display build info
@@ -61,7 +61,7 @@ jobs:
     needs: check_source
     if: needs.check_source.outputs.run_tests == 'true'
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Configure CPython
       run: ./configure --with-pydebug --with-openssl=/usr/local/opt/openssl --prefix=/opt/python-dev
     - name: Build CPython
@@ -79,7 +79,7 @@ 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'