refactor: remove Mergify (#836)

This PR removes Mergify configuration from the repository, eliminating automated pull request merging functionality. The change simplifies the repository's automation setup by removing the Mergify configuration file and its reference from the solution file.

- Removes Mergify configuration file containing automated merge rules
- Updates solution file to exclude the removed Mergify configuration

Author: vbreuss

.github/mergify.yml

@@ -48,7 +48,6 @@ EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = ".github", ".github", "{5E35E265-7110-47A0-9E3E-B5180BBB5AA6}"
 	ProjectSection(SolutionItems) = preProject
 		.github\coverage-settings.xml = .github\coverage-settings.xml
-		.github\mergify.yml = .github\mergify.yml
 		.github\copilot-instructions.md = .github\copilot-instructions.md
 	EndProjectSection
 EndProject