bump actions/checkout from v1 to v2.3.4 (via #68)

Author: dependabot[bot]

.github/workflows/build.yml

@@ -13,7 +13,7 @@ jobs:
   build71:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2.3.4
       - uses: shivammathur/setup-php@v2
         with:
           php-version: '7.1.3'
@@ -26,7 +26,7 @@ jobs:
   build72:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2.3.4
       - uses: shivammathur/setup-php@v2
         with:
           php-version: '7.2'
@@ -39,7 +39,7 @@ jobs:
   build73:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2.3.4
       - uses: shivammathur/setup-php@v2
         with:
           php-version: '7.3'
@@ -52,7 +52,7 @@ jobs:
   build74:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2.3.4
       - uses: shivammathur/setup-php@v2
         with:
           php-version: '7.4'
@@ -65,7 +65,7 @@ jobs:
   build80:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2.3.4
       - uses: shivammathur/setup-php@v2
         with:
           php-version: '8.0'