fix: Avoid adding a null value to concat() function for cache behaviors local variable

[bryantbiggs]

Description

• Avoid adding a null value to concat() function for cache behaviors local variable

Motivation and Context

• Resolves [Bug] ordered_cache_behavior not present throwing an error #178

Breaking Changes

• No

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

[flora-five]

I have created #181, to remove the constraint that the default_cache_behavior variable cannot be null. It includes this fix because it affects the same code. Would you consider it to supersede this PR?

[bryantbiggs]

no - that doesn't make sense since its a required argument https://github.com/hashicorp/terraform-provider-aws/blob/8927020aa6b462f30ecb8caed61308f2aa3f59d6/internal/service/cloudfront/distribution.go#L105-L107

[antonbabenko]

This PR is included in version 6.0.1 🎉

[github-actions]

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