Fix torch nightly versions (#258)

Summary:
Pull Request resolved: #258

Error on installing required packages because an invalid nightly build is specified.

`ERROR: No matching distribution found for torchvision==0.17.0.dev20230907`

Reviewed By: digantdesai, huydhn

Differential Revision: D49117775

fbshipit-source-id: d3288c21d35de7c9c3eeaf9c5f2fd62db8affcd3

Author: guangy10

.ci/docker/ci_commit_pins/nightly.txt

@@ -1 +1 @@
-dev20230907
+dev20230908

install_requirements.sh

@@ -17,7 +17,7 @@ pip install .
 # models in executorch/examples/models.
 # The version in this file will be the correct version for the
 # corresponsing version of the repo.
-NIGHTLY_VERSION=dev20230907
+NIGHTLY_VERSION=dev20230908
 
 TORCH_VERSION=2.2.0.${NIGHTLY_VERSION}
 pip install --force-reinstall --pre torch=="${TORCH_VERSION}" -i https://download.pytorch.org/whl/nightly/cpu