Specify version when installing WiX

Update our CI job and build instructions with the latest WiX version, so
that we don't encounter any installation issues when new WiX versions
are released.

Also, add a reminder in our release instruction to bump the WiX version
before we start a new release.

Fixes #1087

.well-known/funding-manifest-urls

@@ -1 +0,0 @@
-https://dangerzone.rocks/assets/json/funding.json

RELEASE.md

@@ -10,7 +10,7 @@ Here is a list of tasks that should be done before issuing the release:
       You can generate its content with the the `poetry run ./dev_scripts/generate-release-tasks.py` command.
 - [ ] [Add new Linux platforms and remove obsolete ones](https://github.com/freedomofpress/dangerzone/blob/main/RELEASE.md#add-new-linux-platforms-and-remove-obsolete-ones)
 - [ ] Bump the Python dependencies using `poetry lock`
-- [ ] Check for new [WiX releases](https://github.com/wixtoolset/wix/releases) and update it if needed
+- [ ] Check for new [WiX releases](https://github.com/wixtoolset/wix/releases)
 - [ ] Update `version` in `pyproject.toml`
 - [ ] Update `share/version.txt`
 - [ ] Update the "Version" field in `install/linux/dangerzone.spec`