fix(google_cloudsql_mysql): switching from coalesce to concat

[izo3]

Description

Replace coalescelist with concat in replica_names local to prevent "no non-null arguments" error when replica_count = 0 and custom_replica_name is empty (non-prod default). concat safely returns empty list instead of failing.

For example under common-voice:

│ 
│   on .terraform/modules/database.mysql_database/google_cloudsql_mysql/main.tf line 15, in locals:
│   15:   replica_names        = coalescelist(var.custom_replica_name, [for index in range(var.replica_count) : "${local.default_replica_name}-${index}"])
│     ├────────────────
│     │ while calling coalescelist(vals...)
│     │ local.default_replica_name is "common-voice-nonprod-sandbox-v2-replica"
│     │ var.custom_replica_name is empty list of string
│     │ var.replica_count is 0
│ 
│ Call to function "coalescelist" failed: no non-null arguments.

Related Tickets & Documents

• SVCSE-4188

[github-actions]

Release plan

Directory	Previous version	New version
google_cloudsql_mysql	1.0.0	1.0.1