Fix docker build issue after 164575 (pytorch#164779)

Fix docker build issue after 164575 (pytorch#164774)

Looks like pytorch#164575 introduced an issue.
The command is wrong:
```
conda install -c "whl/nightly" -y python=3.11 conda=25.7.0
```
Should be just using default conda channel:
```
conda install  -y python=3.11 conda=25.7.0
```

Pull Request resolved: pytorch#164774
Approved by: https://github.com/Camyll

(cherry picked from commit c1f40d3)

Co-authored-by: atalman <[email protected]>

Author: pytorchbot

Dockerfile

@@ -53,7 +53,7 @@ ARG CUDA_PATH=cu121
 ARG INSTALL_CHANNEL=whl/nightly
 # Automatically set by buildx
 # pinning version of conda here see: https://github.com/pytorch/pytorch/issues/164574
-RUN /opt/conda/bin/conda install -c "${INSTALL_CHANNEL}" -y python=${PYTHON_VERSION} conda=25.7.0
+RUN /opt/conda/bin/conda install -y python=${PYTHON_VERSION} conda=25.7.0
 
 ARG TARGETPLATFORM