Remove static field modifier

Author: MaggieKimani1

src/Microsoft.OpenApi/Services/OpenApiWalker.cs

@@ -18,7 +18,7 @@ namespace Microsoft.OpenApi.Services
     /// </summary>
     public class OpenApiWalker
     {
-        private static OpenApiDocument HostDocument;
+        private OpenApiDocument _hostDocument;
         private readonly OpenApiVisitorBase _visitor;
         private readonly Stack<JsonSchema> _schemaLoop = new Stack<JsonSchema>();
         private readonly Stack<OpenApiPathItem> _pathItemLoop = new Stack<OpenApiPathItem>();
@@ -42,7 +42,7 @@ public void Walk(OpenApiDocument doc)
                 return;
             }
 
-            HostDocument = doc;
+            _hostDocument = doc;
             _schemaLoop.Clear();
             _pathItemLoop.Clear();
 
@@ -902,9 +902,9 @@ internal JsonSchema Walk(JsonSchema schema, bool isComponent = false)
                         Walk(key, () => newSchema = Walk(item.Value));
                         props.Add(key, newSchema);
                         schema = builder.Properties(props);
-                        if (HostDocument != null)
+                        if (_hostDocument != null)
                         {
-                            schema.BaseUri = HostDocument.BaseUri;
+                            schema.BaseUri = _hostDocument.BaseUri;
                         }
                     }
                 });