refactor: remove explicit PR build pipeline

 It is replaced with the "Testably.Server" action

Author: vbreuss

.github/workflows/pr.yml

@@ -38,7 +38,6 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "workflows", "workflows", "{
 	ProjectSection(SolutionItems) = preProject
 		.github\workflows\build.yml = .github\workflows\build.yml
 		.github\workflows\ci.yml = .github\workflows\ci.yml
-		.github\workflows\pr.yml = .github\workflows\pr.yml
 	EndProjectSection
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{B66A0B3F-6A00-482E-99E2-27D8DECB075E}"