feat: use github.action_path instead of donwloading the script from main branch

https://docs.github.com/en/actions/learn-github-actions/contexts#github-context

> github.action_path string
> The path where your action is located.
> You can use this path to easily access files located in the same repository as your action.
> This attribute is only supported in composite actions.

* You don't have to download the script, because you can access to the script with `github.action_path`
* Downloading the script from main branch isn't good. main branch is unreleased and Even if you pin the Action's version, Action may be broken suddenly

Author: suzuki-shunsuke

action.yml

@@ -8,7 +8,7 @@ inputs:
 runs:
   using: "composite"
   steps:
-    - run: curl -sfL https://raw.githubusercontent.com/shmokmt/actions-setup-tfcmt/main/install.sh | sudo sh -s  -- -b /usr/local/bin -d ${TFCMT_VERSION}
+    - run: sudo bash ${{ github.action_path }}/install.sh -b /usr/local/bin -d ${TFCMT_VERSION}
       shell: bash
       env:
         TFCMT_VERSION: ${{ inputs.version }}