From a deadlocked run...

```
#0  0x00007f8a5d48dccd in __lll_lock_wait () from /lib64/libpthread.so.0
#1  0x00007f8a5d486f05 in pthread_mutex_lock () from /lib64/libpthread.so.0
#2  0x00007f8a566e7e89 in arrow::internal::FnOnce<void ()>::FnImpl<arrow::Future<Aws::Utils::Outcome<Aws::S3::Model::ListObjectsV2Result, Aws::S3::S3Error> >::Callback<arrow::fs::(anonymous namespace)::TreeWalker::ListObjectsV2Handler> >::invoke() () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so
#3  0x00007f8a5650efa0 in arrow::FutureImpl::AddCallback(arrow::internal::FnOnce<void ()>) () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so
#4  0x00007f8a566e67a9 in arrow::fs::(anonymous namespace)::TreeWalker::ListObjectsV2Handler::SpawnListObjectsV2() () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so
#5  0x00007f8a566e723f in arrow::fs::(anonymous namespace)::TreeWalker::WalkChild(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, int) () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so
#6  0x00007f8a566e827d in arrow::internal::FnOnce<void ()>::FnImpl<arrow::Future<Aws::Utils::Outcome<Aws::S3::Model::ListObjectsV2Result, Aws::S3::S3Error> >::Callback<arrow::fs::(anonymous namespace)::TreeWalker::ListObjectsV2Handler> >::invoke() () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so
#7  0x00007f8a5650efa0 in arrow::FutureImpl::AddCallback(arrow::internal::FnOnce<void ()>) () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so
#8  0x00007f8a566e67a9 in arrow::fs::(anonymous namespace)::TreeWalker::ListObjectsV2Handler::SpawnListObjectsV2() () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so
#9  0x00007f8a566e723f in arrow::fs::(anonymous namespace)::TreeWalker::WalkChild(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, int) () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so
#10 0x00007f8a566e74b1 in arrow::fs::(anonymous namespace)::TreeWalker::DoWalk() () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so
```

The callback `ListObjectsV2Handler` is being called recursively and the mutex is non-reentrant thus deadlock.

To fix it I got rid of the mutex on `TreeWalker` by using `arrow::util::internal::TaskGroup` instead of manually tracking the #/status of in-flight requests.

Closes apache#9842 from westonpace/bugfix/arrow-12040

Lead-authored-by: Weston Pace <weston.pace@gmail.com>
Co-authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>

…ation (apache#13579)

When locally building the `conda-cpp-valgrind` docker image I've realised we are prompting for confirmation:

```
#10 12.35 Confirm changes: [Y/n] 
#10 88.01  
```
We should use the -y flag when using mamba install:
```
  -y, --yes             Do not ask for confirmation.
```
With this change we are no longer seeing the `Confirm changes` message from mamba.

Authored-by: Raúl Cumplido <raulcumplido@gmail.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>