[GitHub Actions] upgrade/pin versions of ubuntu and actions/setup-go

.github/workflows/auto-approve.yml

@@ -3,7 +3,7 @@ on: pull_request
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
     - uses: hmarr/[email protected]
       with:

.github/workflows/automerge.yml

@@ -13,13 +13,13 @@ on:
   pull_request_review:
     types:
       - submitted
-  check_suite: 
+  check_suite:
     types:
       - completed
   status: {}
 jobs:
   automerge:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - name: automerge
         uses: "pascalgn/automerge-action@135f0bdb927d9807b5446f7ca9ecc2c51de03c4a"

.github/workflows/test.yml

@@ -6,9 +6,9 @@ on:
 name: test
 jobs:
   test:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
-    - uses: actions/setup-go@v1
+    - uses: actions/setup-go@v2
       with:
         go-version: 1.13.x
     - uses: actions/checkout@v2