fix(op_crates/fetch): ensure Request.method to be string (denoland#8100)

Ensure "Request.method" to be the default value ("GET") if 
"init.method" is not defined, which follows browser's behavior.

cli/tests/unit/request_test.ts

@@ -41,6 +41,10 @@ unitTest(function requestNonString(): void {
   assertEquals(new Request(nonString).url, "http://foo/");
 });
 
+unitTest(function methodNonString(): void {
+  assertEquals(new Request("http://foo/", { method: undefined }).method, "GET");
+});
+
 unitTest(function requestRelativeUrl(): void {
   // TODO(nayeemrmn): Base from `--location` when implemented and set.
   assertThrows(() => new Request("relative-url"), TypeError, "Invalid URL.");

op_crates/fetch/26_fetch.js

@@ -990,7 +990,7 @@
         this.url = new URL(String(input)).href;
       }
 
-      if (init && "method" in init) {
+      if (init && "method" in init && init.method) {
         this.method = normalizeMethod(init.method);
       }