Copy escapeReservedWord implementation from python generator (#20035)

Author: andlien

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PythonFastAPIServerCodegen.java

@@ -326,4 +326,12 @@ public void postProcess() {
 
     @Override
     public String generatorLanguageVersion() { return "3.7"; }
+
+    @Override
+    public String escapeReservedWord(String name) {
+        if (this.reservedWordsMappings().containsKey(name)) {
+            return this.reservedWordsMappings().get(name);
+        }
+        return "var_" + name;
+    }
 }