Fix Windows CI: Escape backslashes in JSON path interpolation

Fixes Windows CI failure where file paths with backslashes in JSON strings
were not properly escaped, causing JSON parsing errors.

Changes:
- Escape backslashes in outputPath interpolation for integration tests
- Use .Replace('\', '\\') to convert single backslashes to double backslashes
- Fixes both CliWorkflow tests that create JSON config files with paths

This resolves the System.Text.Json.JsonException on Windows CI builds
while maintaining compatibility with Unix-style paths on macOS/Linux.

Author: jbrinkman

tests/DotNetApiDiff.Tests/Integration/CliWorkflowTests.cs

@@ -515,7 +515,7 @@ public void CliWorkflow_ConfigurationJsonEnumParsing_ShouldParseOutputFormatCorr
             "treatSignatureChangeAsBreaking": true
           },
           "outputFormat": "Html",
-          "outputPath": "{{outputFile}}",
+          "outputPath": "{{outputFile.Replace("\\", "\\\\")}}",
           "failOnBreakingChanges": false
         }
         """;
@@ -597,7 +597,7 @@ public void CliWorkflow_CommandLineOverridesConfig_ShouldUseExplicitCommandLineF
             "treatSignatureChangeAsBreaking": true
           },
           "outputFormat": "Html",
-          "outputPath": "{{outputFile}}",
+          "outputPath": "{{outputFile.Replace("\\", "\\\\")}}",
           "failOnBreakingChanges": false
         }
         """;