fix: Replace try() with can(coalesce()) to better handle null values

[fatmcgav]

Description

The default behaviour of try will return a null value if present. So update the logic to use can(coalesce()) which will ignore a null value.

Motivation and Context

Using the following listeners value, I was getting the below error:

listeners = {
      + http_https_redirect_listener = {
          + port     = 80
          + protocol = "HTTP"
          + redirect = {
              + port        = "443"
              + protocol    = "HTTPS"
              + status_code = "HTTP_301"
            }
        }
      + https                        = {
          + fixed_response = {
              + content_type = "text/plain"
              + message_body = ""
              + status_code  = "404"
            }
          + forward        = null
          + port           = 443
          + protocol       = "HTTPS"
          + rules          = {}
        }
    }

Error:

│ Error: Invalid Attribute Combination
│
│ Either "default_action[1].target_group_arn" or "default_action[1].forward" must be specified when "default_action[1].type" is "forward".
│ default_action[1].type
│
│   with module.alb.module.alb.aws_lb_listener.this["https"],
│   on .terraform/modules/alb.alb/main.tf line 88, in resource "aws_lb_listener" "this":
│   88: resource "aws_lb_listener" "this" {
│

Breaking Changes

None

How Has This Been Tested?

• I have updated at least one of the examples/* to demonstrate and validate my change(s)
• I have tested and validated these changes using one or more of the provided examples/* projects

• I have executed pre-commit run -a on my pull request

[bryantbiggs]

lets start with a reproduction of the issue first

[fatmcgav]

@bryantbiggs I've stuck a simple reproducer here, albeit with a slightly different error being returned by Terraform.

The changes in this PR fix the issue though...