Fix the following compiler (clang 11) warning

python/_jsonnet.c:150:19: warning: comparison of integers of different signs: 'int' and 'const size_t' (aka 'const unsigned long') [-Wsign-compare]
    for (i = 0; i < ctx->argc; ++i) {
                ~ ^ ~~~~~~~~~

Change type of index loop (i) to Py_ssize_t like in all other places in the code.
Cast ctx->argc to Py_ssize_t to make them the same type

Useful link https://www.python.org/dev/peps/pep-0353

Author: timp87

python/_jsonnet.c

@@ -147,7 +147,7 @@ static struct JsonnetJsonValue *cpython_native_callback(
     void *ctx_, const struct JsonnetJsonValue * const *argv, int *succ)
 {
     const struct NativeCtx *ctx = ctx_;
-    int i;
+    Py_ssize_t i;
 
     PyEval_RestoreThread(*ctx->py_thread);
 
@@ -156,7 +156,7 @@ static struct JsonnetJsonValue *cpython_native_callback(
 
     // Populate python function args.
     arglist = PyTuple_New(ctx->argc);
-    for (i = 0; i < ctx->argc; ++i) {
+    for (i = 0; i < (Py_ssize_t) ctx->argc; ++i) {
         double d;
         const char *param_str = jsonnet_json_extract_string(ctx->vm, argv[i]);
         int param_null = jsonnet_json_extract_null(ctx->vm, argv[i]);