`make serve` fails in freshly installed conda environment

[schlunma]

Describe the bug

After installing a dev environment with conda env create -f environment.yml -n esmvaltool_tutorial, I get the following error when running make serve.

$ make serve
bundle install --path .vendor/bundle && bundle update && bundle exec jekyll serve
The `--path` flag has been removed because it relied on being remembered across bundler invocations, which bundler no longer does. Instead please use `bundle config set path '.vendor/bundle'`, and stop using this flag
make: *** [Makefile:49: serve] Error 15

Performing the recommended change in the Makefile kind of works, but gives another error further down:

bundler: failed to load command: jekyll (/home/manuel/ESMValTool_Tutorial/.vendor/bundle/ruby/4.0.0/bin/jekyll)