Build will fail when the only contract is an lsig

[CiottiGiorgio]

algokit-python-template/template_content/smart_contracts/_helpers/build.py.jinja

Line 48 in 42feefa

for app_spec_file_name in app_spec_file_names:

This line will generate an error in the build command when there are no ARC-32 files. This can happen when the only contract is an lsig.