Dockerfile: Use 'SHELL' command to set default shell

This commit updates the Dockerfile to use the `SHELL` command to set the
default shell to bash.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

Dockerfile

@@ -5,8 +5,8 @@ ARG CMAKE_VERSION=3.30.5
 ARG UID=1001
 ARG GID=1001
 
-# Make bash the default shell
-ENV SHELL=/bin/bash
+# Set default shell during Docker image build to bash
+SHELL ["/bin/bash", "-c"]
 
 # Install packages
 RUN apt-get clean