website: Update GitHub Actions example for setup-go@v4 and using go.mod version (#169)

Reference: https://github.com/actions/setup-go#getting-go-version-from-the-gomod-file

This prevents developers from needing to continually update their testing workflow with Go upgrades, which can be pointed at the minimum Go version as defined by their Go module.

Author: bflad

website/docs/plugin/testing/acceptance-tests/index.mdx

@@ -136,7 +136,7 @@ Create a [GitHub Actions workflow](https://docs.github.com/en/actions/using-work
 
 Use the [`matrix`](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idstrategymatrix) strategy for more advanced configuration, such as running acceptance testing against multiple Terraform CLI versions.
 
-The following example workflow runs acceptance testing for the provider using the latest patch versions of Go 1.19 and Terraform CLI 1.3:
+The following example workflow runs acceptance testing for the provider using the latest patch versions of the Go version in the `go.mod` file and Terraform CLI 1.5:
 
 ```yaml
 name: Terraform Provider Tests
@@ -157,12 +157,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: actions/setup-go@v3
+      - uses: actions/setup-go@v4
         with:
-          go-version: '1.19'
+          go-version-file: 'go.mod'
       - uses: hashicorp/setup-terraform@v2
         with:
-          terraform_version: '1.3.*'
+          terraform_version: '1.5.*'
           terraform_wrapper: false
       - run: go test -v -cover ./...
         env:
@@ -172,14 +172,14 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: actions/setup-go@v3
+      - uses: actions/setup-go@v4
         with:
-          go-version: '1.19'
+          go-version-file: 'go.mod'
       - run: go test -v -cover ./...
 ```
 
 
-The following example workflow runs acceptance testing for the provider using the latest patch versions of Go 1.19 and Terraform CLI 0.12 through 1.3:
+The following example workflow runs acceptance testing for the provider using the latest patch versions of Go version in the `go.mod` file and Terraform CLI 0.12 through 1.5:
 
 ```yaml
 name: Terraform Provider Tests
@@ -210,11 +210,13 @@ jobs:
           - '1.1.*'
           - '1.2.*'
           - '1.3.*'
+          - '1.4.*'
+          - '1.5.*'
     steps:
       - uses: actions/checkout@v3
-      - uses: actions/setup-go@v3
+      - uses: actions/setup-go@v4
         with:
-          go-version: '1.19'
+          go-version-file: 'go.mod'
       - uses: hashicorp/setup-terraform@v2
         with:
           terraform_version: ${{ matrix.terraform-version }}
@@ -227,9 +229,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: actions/setup-go@v3
+      - uses: actions/setup-go@v4
         with:
-          go-version: '1.19'
+          go-version-file: 'go.mod'
       - run: go test -v -cover ./...
 ```