CI: switch to checkout v2

this might fix occasional reference is not a tree errors.

diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index f9ee3ba096736d57d47dc632fb08893d2e59055b..acfa6114ab9dc5d0410697b804d8fa4d647b5885 100644 (file)
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -8,7 +8,7 @@ jobs:
     runs-on: [ubuntu-18.04]
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: setup
       run: |
         sudo apt-get install gfortran libopenmpi-dev openmpi-common openmpi-bin libblas-dev liblapack-dev libblas3 liblapack3
@@ -27,7 +27,7 @@ jobs:
     runs-on: [macos-latest]
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: info
       run: |
         g++ -v
@@ -43,7 +43,7 @@ jobs:
     runs-on: [macos-latest]
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: setup
       run: |
         brew install openmpi