.github/workflows: Add Terraform 1.3.x to testing matrix (#226)

Reference: https://github.com/hashicorp/terraform/releases/tag/v1.3.0

Author: bflad

.github/workflows/ci-go.yml

@@ -62,6 +62,7 @@ jobs:
           - '1.0.*'
           - '1.1.*'
           - '1.2.*'
+          - '1.3.*'
   terraform-provider-corner-tfprotov6:
     defaults:
       run:
@@ -97,6 +98,7 @@ jobs:
           - '1.0.*'
           - '1.1.*'
           - '1.2.*'
+          - '1.3.*'
   test:
     name: test (Go v${{ matrix.go-version }})
     runs-on: ubuntu-latest