Fix GitHub Workflow badges

[GromNaN]

Documentation: https://docs.github.com/en/actions/how-tos/monitor-workflows/add-a-status-badge

[Copilot]

Pull Request Overview

This PR updates GitHub Actions workflow badges in the README to use the current recommended URL format that references specific workflow files instead of workflow names.

• Updated badge URLs to reference workflow files directly (tests.yml and coding-standards.yml)
• Changed from the deprecated workflow name-based URL format to the file-based format

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.73%. Comparing base (c9ddfcb) to head (f735a84).
⚠️ Report is 4 commits behind head on v2.x.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##               v2.x    #1785   +/-   ##
=========================================
  Coverage     87.73%   87.73%           
  Complexity     3194     3194           
=========================================
  Files           424      424           
  Lines          6352     6352           
=========================================
  Hits           5573     5573           
  Misses          779      779           

Flag	Coverage Δ
6.0-replica_set	85.68% <ø> (ø)
6.0-server	81.70% <ø> (ø)
6.0-sharded_cluster	85.28% <ø> (ø)
8.0-replica_set	87.65% <ø> (ø)
8.0-server	82.58% <ø> (ø)
8.0-sharded_cluster	87.32% <ø> (ø)

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