Don't drop :exclusions when running neil dep add or neil dep upgrade

[teodorlu]

Please answer the following questions and leave the below in as part of your PR.

• This PR corresponds to an issue with a clear problem statement.

  • neil dep upgrade drops dep :exclusions #183

• I have updated the CHANGELOG.md file with a description of the addressed issue.

[teodorlu]

This is the test that fails:

https://github.com/teodorlu/neil/blob/ab7e5ffa92bbdb3dcbeac26a4fe6da985487faa6/test/babashka/neil/dep_upgrade_test.clj#L133

A deps.edn file that had a :sha version keeps that version around (per ab7e5ff). Example:

$ cat deps.edn 
{:deps {clj-kondo/clj-kondo
                            {:git/url "https://github.com/clj-kondo/clj-kondo"
                             :sha "6ffc3934cb83d2c4fff16d84198c73b40cd8a078"}}}
$ neil-dev dep upgrade
:action "upgrading" :lib clj-kondo/clj-kondo :current-version nil :sha 8d1531b23485815ab26a7da10eac9950ecc2338d
$ cat deps.edn 
{:deps {clj-kondo/clj-kondo
                            {:git/url "https://github.com/clj-kondo/clj-kondo"
                             :sha "6ffc3934cb83d2c4fff16d84198c73b40cd8a078"
                             :git/sha "8d1531b23485815ab26a7da10eac9950ecc2338d"}}}

bad!
This even causes clj to error:

$ clj
Error building classpath. git coord has both :sha and :git/sha for clj-kondo/clj-kondo

[teodorlu]

How about using reference-style markdown links for CHANGELOG.md?

Currently, we write the CHANGELOG like this (scroll right):

- [#181](https://github.com/babashka/neil/issues/181): fix `neil --version`
- fix tests by referring to latest hiccup ([@teodorlu](https://github.com/teodorlu))
- [#180](https://github.com/babashka/neil/issues/180): `neil dep upgrade`: allow upgrading from an unstable version to the latest unstable version ([@teodorlu](https://github.com/teodorlu))
- [#180](https://github.com/babashka/neil/issues/180): `neil dep upgrade`: with `--unstable`, opt-into unstable library updates ([@teodorlu](https://github.com/teodorlu))
- [#183](https://github.com/babashka/neil/issues/183): Don't drop `:exclusions` when running `neil dep add` or `neil dep upgrade` ([@borkdude](https://github.com/borkdude) and [@teodorlu](https://github.com/teodorlu))

With the proposed link format, we'd write the CHANGELOG like this (scroll right):

- [#181](https://github.com/babashka/neil/issues/181): fix `neil --version`
- fix tests by referring to latest hiccup ([@teodorlu])
- [#180](https://github.com/babashka/neil/issues/180): `neil dep upgrade`: allow upgrading from an unstable version to the latest unstable version ([@teodorlu])
- [#180](https://github.com/babashka/neil/issues/180): `neil dep upgrade`: with `--unstable`, opt-into unstable library updates ([@teodorlu])
- [#183](https://github.com/babashka/neil/issues/183): Don't drop `:exclusions` when running `neil dep add` or `neil dep upgrade` ([@borkdude] and [@teodorlu])

[@borkdude]: https://github.com/borkdude
[@teodorlu]: https://github.com/teodorlu

That way, we can write [@borkdude] and have the link to https://github.com/borkdude/ work automatically. Thoughts?

[borkdude]

I'm using script/changelog.clj to render these links after typing, but if your suggested way renders the exact same way, I'd be down with that.

[borkdude]

Thanks a lot!