chore: fix build errors for kotlin and dotnet

Author: ChiragAgg5k

templates/dotnet/Package/Client.cs.twig

@@ -149,9 +149,8 @@ namespace {{ spec.title | caseUcfirst }}
                 new HttpMethod(method),
                 _endpoint + path + queryString);
 
-            if ("multipart/form-data".Equals(
-                headers["content-type"],
-                StringComparison.OrdinalIgnoreCase))
+            if (headers.TryGetValue("content-type", out var contentType) && 
+                "multipart/form-data".Equals(contentType, StringComparison.OrdinalIgnoreCase))
             {
                 var form = new MultipartFormDataContent();
 

templates/kotlin/src/main/kotlin/io/appwrite/services/ServiceTemplate.kt.twig

@@ -55,7 +55,7 @@ class {{ service.name | caseUcfirst }}(client: Client) : Service(client) {
             "{{ parameter.name }}" to {{ parameter.name | caseCamel }},
         {%~ endfor %}
         )
-        val apiHeaders = mutableMapOf(
+        val apiHeaders = mutableMapOf<String, String>(
         {%~ for key, header in method.headers %}
             "{{ key }}" to "{{ header }}",
         {%~ endfor %}