chore: update go templates (aws#21728)

These changes were brought up in a [review of the Go workshop](aws-samples/aws-cdk-intro-workshop#636)

- update Go version
- close jsii process
- remove unneeded `assertions` alias

----

### All Submissions:

* [ ] Have you followed the guidelines in our [Contributing guide?](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md)

### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/main/INTEGRATION_TESTS.md)?
	* [ ] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk/lib/init-templates/app/go/%name%.template.go

@@ -29,6 +29,8 @@ func New%name.PascalCased%Stack(scope constructs.Construct, id string, props *%n
 }
 
 func main() {
+	defer jsii.Close()
+
 	app := awscdk.NewApp(nil)
 
 	New%name.PascalCased%Stack(app, "%name.PascalCased%Stack", &%name.PascalCased%StackProps{

packages/aws-cdk/lib/init-templates/app/go/%name%_test.template.go

@@ -4,7 +4,7 @@ package main
 // 	"testing"
 
 // 	"github.com/aws/aws-cdk-go/awscdk/v2"
-// 	assertions "github.com/aws/aws-cdk-go/awscdk/v2/assertions"
+// 	"github.com/aws/aws-cdk-go/awscdk/v2/assertions"
 // 	"github.com/aws/jsii-runtime-go"
 // )
 

packages/aws-cdk/lib/init-templates/app/go/go.template.mod

@@ -1,6 +1,6 @@
 module %name%
 
-go 1.16
+go 1.18
 
 require (
   github.com/aws/aws-cdk-go/awscdk/v2 v%cdk-version%

packages/aws-cdk/lib/init-templates/sample-app/go/%name%.template.go

@@ -32,6 +32,8 @@ func New%name.PascalCased%Stack(scope constructs.Construct, id string, props *%n
 }
 
 func main() {
+	defer jsii.Close()
+
 	app := awscdk.NewApp(nil)
 
 	New%name.PascalCased%Stack(app, "%name.PascalCased%Stack", &%name.PascalCased%StackProps{

packages/aws-cdk/lib/init-templates/sample-app/go/%name%_test.template.go

@@ -4,7 +4,7 @@ import (
 	"testing"
 
 	"github.com/aws/aws-cdk-go/awscdk/v2"
-	assertions "github.com/aws/aws-cdk-go/awscdk/v2/assertions"
+	"github.com/aws/aws-cdk-go/awscdk/v2/assertions"
 	"github.com/aws/jsii-runtime-go"
 )
 

packages/aws-cdk/lib/init-templates/sample-app/go/go.template.mod

@@ -1,6 +1,6 @@
 module %name%
 
-go 1.16
+go 1.18
 
 require (
   github.com/aws/aws-cdk-go/awscdk/v2 v%cdk-version%