Escape backticks in stdout and stderr

I'm using the workflow in the README.

Show Workflow

```yaml
defaults:
run:
working-directory: ${{ env.tf_actions_working_dir }}
permissions:
pull-requests: write
steps:
- uses: actions/checkout@v4
- uses: hashicorp/setup-terraform@v3

- name: Terraform fmt
id: fmt
run: terraform fmt -check
continue-on-error: true

- name: Terraform Init
id: init
run: terraform init

- name: Terraform Validate
id: validate
run: terraform validate -no-color

- name: Terraform Plan
id: plan
run: terraform plan -no-color
continue-on-error: true

- uses: actions/github-script@v6
if: github.event_name == 'pull_request'
env:
PLAN: "terraform\n${{ steps.plan.outputs.stdout }}"
with:
github-token: ${{ secrets.GITHUB_TOKEN }}
script: |
const output = `#### Terraform Format and Style 🖌\`${{ steps.fmt.outcome }}\`
#### Terraform Initialization ⚙️\`${{ steps.init.outcome }}\`
#### Terraform Validation 🤖\`${{ steps.validate.outcome }}\`
Validation Output

\`\`\`\n
${{ steps.validate.outputs.stdout }}
\`\`\`

#### Terraform Plan 📖\`${{ steps.plan.outcome }}\`

Show Plan

\`\`\`\n
${process.env.PLAN}
\`\`\`

*Pusher: @${{ github.actor }}, Action: \`${{ github.event_name }}\`, Working Directory: \`${{ env.tf_actions_working_dir }}\`, Workflow: \`${{ github.workflow }}\`*`;

github.rest.issues.createComment({
issue_number: context.issue.number,
owner: context.repo.owner,
repo: context.repo.repo,
body: output
})
```

---

CI failed when upgrading the AWS provider.

```
SyntaxError: Unexpected identifier 'compute_environments_order'
at new AsyncFunction ()
at callAsyncFunction (/home/runner/work/_actions/actions/github-script/v7/dist/index.js:35424:16)
at main (/home/runner/work/_actions/actions/github-script/v7/dist/index.js:35522:26)
at /home/runner/work/_actions/actions/github-script/v7/dist/index.js:35497:1
at /home/runner/work/_actions/actions/github-script/v7/dist/index.js:35553:3
at Object. (/home/runner/work/_actions/actions/github-script/v7/dist/index.js:35556:12)
at Module._compile (node:internal/modules/cjs/loader:1241:14)
at Module._extensions..js (node:internal/modules/cjs/loader:1295:10)
at Module.load (node:internal/modules/cjs/loader:1091:32)
at Module._load (node:internal/modules/cjs/loader:938:12)
Error: Unhandled error: SyntaxError: Unexpected identifier 'compute_environments_order'
```

The cause was that backticks were used in the stdout of warnings. Backticks must be escaped.

```
Warning: Attribute Deprecated

with aws_batch_job_queue.example,
on batch_job_queue.tf line 5, in resource "aws_batch_job_queue" "example":
5: compute_environments = [aws_batch_compute_environment.example.arn]

This parameter will be replaced by `compute_environments_order`.

(and 3 more similar warnings elsewhere)
```