fetch: Change wording of "Body is unusable" error

lib/web/fetch/body.js

@@ -406,7 +406,7 @@ async function consumeBody (object, convertBytesToJSValue, instance) {
   // 1. If object is unusable, then return a promise rejected
   //    with a TypeError.
   if (bodyUnusable(object[kState].body)) {
-    throw new TypeError('Body is unusable')
+    throw new TypeError('Body is unusable: Body has already been read')
   }
 
   throwIfAborted(object[kState])

test/fetch/client-fetch.js

@@ -370,7 +370,7 @@ test('locked blob body', (t, done) => {
     const res = await fetch(`http://localhost:${server.address().port}`)
     const reader = res.body.getReader()
     res.blob().catch(err => {
-      strictEqual(err.message, 'Body is unusable')
+      strictEqual(err.message, 'Body is unusable: Body has already been read')
       reader.cancel()
     }).finally(done)
   })
@@ -390,7 +390,7 @@ test('disturbed blob body', (t, done) => {
       ok(true)
     })
     await res.blob().catch(err => {
-      strictEqual(err.message, 'Body is unusable')
+      strictEqual(err.message, 'Body is unusable: Body has already been read')
     })
     done()
   })

test/node-fetch/main.js

@@ -1385,7 +1385,7 @@ describe('node-fetch', () => {
       assert.strictEqual(res.headers.get('content-type'), 'text/plain')
       return res.text().then(() => {
         assert.strictEqual(res.bodyUsed, true)
-        return assert.rejects(res.text(), new TypeError('Body is unusable'))
+        return assert.rejects(res.text(), new TypeError('Body is unusable: Body has already been read'))
       })
     })
   })