Fix submodule checkout issue

[wata727]

A few days ago, aws-sdk-go submodule checkout failed with the following error:

  /usr/bin/git submodule sync
  /usr/bin/git -c protocol.version=2 submodule update --init --force --depth=1
  Submodule 'rules/models/aws-sdk-go' (https://github.com/aws/aws-sdk-go) registered for path 'rules/models/aws-sdk-go'
  Cloning into '/home/runner/work/tflint-ruleset-aws/tflint-ruleset-aws/rules/models/aws-sdk-go'...
  remote: app=lariat msg="[FATAL]: Internal error"        
  remote: aborting due to possible repository corruption on the remote side.
  Error: fatal: early EOF
  Error: fatal: fetch-pack: invalid index-pack output
  Error: fatal: clone of 'https://github.com/aws/aws-sdk-go' into submodule path '/home/runner/work/tflint-ruleset-aws/tflint-ruleset-aws/rules/models/aws-sdk-go' failed

https://github.com/terraform-linters/tflint-ruleset-aws/actions/runs/4214996572/jobs/7316120928

From what I've researched, it seems likely that this is an issue due to repository size. This pull request sets --depth=0 to reduce the repository size to fetch.