Try: fix end 2 end inline tokens test (#12459)

The adding-inline-tokens.test.js test was failing on Travis, instead of an image upload being successful we got an error reporting that no permissions exist.

This commit uses 2 commands on the docker container to do the following actions:
Create an uploads folder inside wp-content.
Change the folder permissions to 766.
766 was chosen because according to the hierarchy we should follow when trying to fix permission problems available in https://codex.wordpress.org/Changing_File_Permissions is the most adequate value. The value bellow it (765) does not work.

bin/install-wordpress.sh

@@ -77,5 +77,9 @@ fi
 echo -e $(status_message "Activating Gutenberg...")
 docker-compose $DOCKER_COMPOSE_FILE_OPTIONS run --rm $CLI plugin activate gutenberg >/dev/null
 
+# Make sure the uploads folder exist and we have permissions to add files there.
+docker-compose $DOCKER_COMPOSE_FILE_OPTIONS run --rm $CONTAINER mkdir -p /var/www/html/wp-content/uploads
+docker-compose $DOCKER_COMPOSE_FILE_OPTIONS run --rm $CONTAINER chmod -v 767 /var/www/html/wp-content/uploads
+
 # Install a dummy favicon to avoid 404 errors.
 docker-compose $DOCKER_COMPOSE_FILE_OPTIONS run --rm $CONTAINER touch /var/www/html/favicon.ico

test/e2e/specs/adding-inline-tokens.test.js

@@ -21,7 +21,7 @@ describe( 'adding inline tokens', () => {
 		await newPost();
 	} );
 
-	it.skip( 'should insert inline image', async () => {
+	it( 'should insert inline image', async () => {
 		// Create a paragraph.
 		await clickBlockAppender();
 		await page.keyboard.type( 'a ' );