fix: use get_gstin_list function for fetching list of gstins in GSTR1 Report (backport #2593)

[mergify]

• default GSTIN was not fetched while setting GSTINs in GSTR-1 report (old)
• Using the common utility to fetch GSTINs.

Frappe Support Issue: https://support.frappe.io/app/hd-ticket/21481

_{Huly®: IC-2712}

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This is an automatic backport of pull request #2593 done by Mergify.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 61.15%. Comparing base (da29fa2) to head (1492320).
Report is 14 commits behind head on version-14-hotfix.

Files with missing lines	Patch %	Lines
india_compliance/gst_india/report/gstr_1/gstr_1.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@                Coverage Diff                 @@
##           version-14-hotfix    #2597   +/-   ##
==================================================
  Coverage              61.14%   61.15%           
==================================================
  Files                    114      114           
  Lines                  11057    11056    -1     
==================================================
  Hits                    6761     6761           
+ Misses                  4296     4295    -1     

Files with missing lines	Coverage Δ
india_compliance/gst_india/report/gstr_1/gstr_1.py	38.27% <50.00%> (+0.05%)	⬆️

[india-compliance-bot]

🎉 This PR is included in version 14.30.5 🎉

The release is available on GitHub release

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