Revert "Pin pt nightly CPU version (#1061)"

This reverts commit 4734eda.

Author: HDCharles

.github/workflows/regression_test.yml

@@ -61,7 +61,7 @@ jobs:
             gpu-arch-version: ""
           - name: CPU Nightly
             runs-on: linux.4xlarge
-            torch-spec: '--pre torch==2.6.0.dev20241010+cpu --index-url https://download.pytorch.org/whl/nightly/cpu'
+            torch-spec: '--pre torch --index-url https://download.pytorch.org/whl/nightly/cpu'
             gpu-arch-type: "cpu"
             gpu-arch-version: ""