fix: aws terraform-tests performance_insights_retention_period

[#187103734](https://www.pivotaltracker.com/story/show/187103734)

Recently, a new PR for validating this property was merged:
hashicorp/terraform-provider-aws#35870

I believe it's valuable to have our tests break when changes
like this are introduced in the providers. Therefore, we should
try have behaviours such as this encoded in our tests. Things
like: "invalid values for property X are not validated by TF".

terraform-tests/mssql_test.go

@@ -739,19 +739,14 @@ var _ = Describe("mssql", Label("mssql-terraform"), Ordered, func() {
 		})
 
 		When("an invalid retention period is passed", func() {
-			It("doesn't detect any errors and plan finishes succesfully", func() {
+			It("should fail and return a descriptive error message", func() {
 				// invalid values for the retention_period are handled by the IAAS not Terraform
-				plan := ShowPlan(terraformProvisionDir, buildVars(defaultVars, requiredVars, map[string]any{
+				session, _ := FailPlan(terraformProvisionDir, buildVars(defaultVars, requiredVars, map[string]any{
 					"performance_insights_enabled":          true,
 					"performance_insights_retention_period": 13,
 				}))
-
-				Expect(AfterValuesForType(plan, "aws_db_instance")).To(
-					MatchKeys(IgnoreExtras, Keys{
-						"performance_insights_enabled":          BeTrue(),
-						"performance_insights_retention_period": BeNumerically("==", 13),
-					}),
-				)
+				Expect(session.ExitCode()).NotTo(Equal(0))
+				Expect(session).To(gbytes.Say("expected performance_insights_retention_period to be divisible by 31, got: 13"))
 			})
 		})
 	})