Version 0.8.4 modifies anaconda-project.yml during prepare

[jlstevens]

While trying to reproduce this issue, I found it is related to the new user_fields field added to version 0.8.4:

$ conda create -n example python
$ conda activate example
$ conda install anaconda-project=0.8.4
$ git clone git@github.com:pyviz-topics/examples.git
$ git checkout evaluated_branch_fix # Adds user_fields to anaconda-project.yml
$ cd examples/iex_trading/
$ anaconda-project prepare --directory .

$ git diff  # anaconda-project.yml has been modified
diff --git a/iex_trading/anaconda-project.yml b/iex_trading/anaconda-project.yml
index b151145..8b68c75 100644
--- a/iex_trading/anaconda-project.yml
+++ b/iex_trading/anaconda-project.yml
@@ -3,36 +3,35 @@
 name: IEX trading
 description: Dashboard visualizing stock trades on the IEX exchange
 maintainers:
-  - jlstevens
+- jlstevens
 labels:
-  - datashader
-  - panel
-  - holoviews
...

Things work as expected in 0.8.3: user_fields is no longer supported and the anaconda-project.yml isn't being modified. I don't yet understand why anaconda-project would even open the anaconda-project.yml in writeable mode when running the prepare command ...