fix: widen github provider constraint to >= 6.11.0, drop stale lock file

CSVD/terraform-github-repo module requires ~> 6.11; workspace had >= 6.6.0, < 6.7.0
which is incompatible. Lock file was pinned to 6.6.0 — delete so terraform init
regenerates it against the updated constraint.

providers.tf

@@ -2,7 +2,7 @@ terraform {
   required_providers {
     github = {
       source  = "integrations/github"
-      version = ">= 6.6.0, < 6.7.0"
+      version = ">= 6.11.0"
     }
     aws = {
       source  = "hashicorp/aws"