Make serve - error message about Gemfiles

## What is the issue?

When running `make serve` or `make serve-quick`, the commands are not failing but show on the top:

```
mv: cannot stat 'Gemfile': No such file or directory
mv: cannot stat 'Gemfile.lock': No such file or directory
```
I am afraid it may be confusing for newcomers.

## How to fix that?

This comes from these lines in `make serve`, `make serve-quick`

```
$(ACTIVATE_ENV) && \
mv Gemfile Gemfile.backup || true && \
mv Gemfile.lock Gemfile.lock.backup || true && \
```

I do not have a good way to fix this

Start with the `make serve` and `make serve-quick` targets and reproduce the commands to observe the Gemfile warnings. Inspect the shown `mv` commands and verify that the completed change runs both targets without displaying missing-Gemfile errors.

Written by the indexing model from the issue text.