Add workflow file

- Add workflow to check that the only branch that can merge to main is dev

.github/workflows/branch-enforcer.yml

@@ -0,0 +1,16 @@
+# Check that the only branch that can merge to "main" is "dev"
+
+name: "Check Branch"
+
+on:
+  pull_request:
+
+jobs:
+  check_branch:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check branch
+        if: github.base_ref == 'main' && github.head_ref != 'dev'
+        run: |
+          echo "ERROR: Can only merge to main branch from dev branch"
+          exit 1

Mathematics.NET.sln

@@ -28,13 +28,14 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = ".github", ".github", "{9EB2
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "workflows", "workflows", "{1B32D7FF-257B-49BB-B495-D64E5E6C4C82}"
 	ProjectSection(SolutionItems) = preProject
+		branch-enforcer.yml = branch-enforcer.yml
 		.github\workflows\codeql.yml = .github\workflows\codeql.yml
 		.github\workflows\generate-documentation-site.yml = .github\workflows\generate-documentation-site.yml
 	EndProjectSection
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Mathematics.NET.DevApp", "src\Mathematics.NET.DevApp\Mathematics.NET.DevApp.csproj", "{89C3482F-0027-483E-AAD7-5E12453915B3}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Mathematics.NET.Renderer", "src\Mathematics.NET.Renderer\Mathematics.NET.Renderer.csproj", "{94744B01-DD3C-4623-992F-19C5CC2B475B}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Mathematics.NET.Renderer", "src\Mathematics.NET.Renderer\Mathematics.NET.Renderer.csproj", "{94744B01-DD3C-4623-992F-19C5CC2B475B}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution