ci: Bump Go version to 1.20

Author: moricho

.github/workflows/action.yml

@@ -8,7 +8,7 @@ jobs:
       - name: set up Go environment
         uses: actions/setup-go@v2
         with:
-          go-version: 1.15
+          go-version: 1.20
       - name: check out
         uses: actions/checkout@v2
       - name: cache

.github/workflows/release.yml

@@ -14,7 +14,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@v2
         with:
-          go-version: 1.15
+          go-version: 1.20
       - name: Run GoReleaser
         uses: goreleaser/goreleaser-action@v2
         with: