test: move test-fs-largefile to sequential

test-fs-largefile is in the pummel directory because it creates a large
file, but the large file (due to the way it is created) does not consume
much disk space and runs quickly on Raspberry Pi devices and everything
else. Move the test to sequential.

test/pummel/test-fs-largefile.js → test/sequential/test-fs-largefile.js

@@ -34,7 +34,7 @@ const fd = fs.openSync(filepath, 'w+');
 const offset = 5 * 1024 * 1024 * 1024; // 5GB
 const message = 'Large File';
 
-fs.truncateSync(fd, offset);
+fs.ftruncateSync(fd, offset);
 assert.strictEqual(fs.statSync(filepath).size, offset);
 const writeBuf = Buffer.from(message);
 fs.writeSync(fd, writeBuf, 0, writeBuf.length, offset);