CI: github actions: checkout@v2

update checkout action to @v2. This should avoid errors when rerunning a
job about "reference is not a tree".

diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 6cbf077e1aff774d4447ff4e9ece0e6ec13c2caa..8e74694e5961e82088ae749d3e6f8cc787fc5ba9 100644 (file)
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -10,7 +10,7 @@ jobs:
     runs-on: [ubuntu-18.04]
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: setup
       run: |
         ./contrib/utilities/download_clang_format
@@ -38,7 +38,7 @@ jobs:
     runs-on: [macos-latest]
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: setup
       run: |
         ./contrib/utilities/download_clang_format
@@ -67,7 +67,7 @@ jobs:
     runs-on: [macos-latest]
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: setup
       run: |
         brew install openmpi