Fixed incorrect relative paths set in index.py

[bensonce]

There was an issue in the latest run of the Update Config Rules workflow:

Writing result to config_rule_data.json.
File not found:  [Errno 2] No such file or directory: '../../managed_rules_locals.tf'
Traceback (most recent call last):
  File "/home/runner/work/terraform-aws-managed-config-rules/terraform-aws-managed-config-rules/scripts/index.py", line 24, in <module>
    for _, local in enumerate(data['locals']):
KeyError: 'locals'
Error: Process completed with exit code 1.

I've updated the file paths to use the scripts directory to build absolute paths to the managed_rules_locals.tf and managed_rules_variables.tf files.

Here is a successful run of the updated workflow: https://github.com/niaid/terraform-aws-managed-config-rules/actions/runs/9208135752/job/25329687982

[duraikkannuv2]

Looks good.