Add Fedora 43 image for source-build

[Copilot]

• Create Fedora 43 directory structure (src/fedora/43/amd64/)
• Create Dockerfile for Fedora 43 based on Fedora 41 from commit 778c786
• Update Fedora manifest.json with correct tag (fedora-43-amd64)
• Verify directory structure matches Fedora 41 pattern
• Build and validate the new image locally
• Address code review feedback (remove duplicate jq package)
• Remove short tag name to match current repository convention
• Run security scanning (CodeQL)
• All tasks completed successfully

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add Fedora 43 image for source-build</issue_title>
<issue_description>Related to dotnet/dotnet#3835.

The Fedora 41 image removed in #1551 should be brought back and upgraded to Fedora 43.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add Fedora 43 image for source-build #1566

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