CI fails to install vnum (again)
https://github.com/py2many/py2many/issues/461 was the last time this happened.

I don't have a CI build, but locally (with `act`) I see a new version of dart, and a similar error to last time.

```
[CI/build-1] ⭐  Run Install dart dependencies
[CI/build-1]   🐳  docker exec cmd=[bash --noprofile --norc -e -o pipefail /var/run/act/workflow/16.sh] user= workdir=
| Dart SDK version: 2.17.1 (stable) (Tue May 17 17:58:21 2022 +0000) on "linux_x64"
| Creating build using template package-simple...
|
|   .gitignore
|   analysis_options.yaml
|   CHANGELOG.md
|   pubspec.yaml
|   README.md
|   example/build_example.dart
|   lib/build.dart
|   lib/src/build_base.dart
|   test/build_test.dart
|
| Created project build in tests/build! In order to get started, run the following commands:
|
|   cd tests/build
|   dart run example/build_example.dart
|
| + dart pub add collection:1.15.0
| Resolving dependencies...
| + _fe_analyzer_shared 40.0.0
| + analyzer 4.1.0
| + args 2.3.1
| + async 2.9.0
| + boolean_selector 2.1.0
| + collection 1.15.0 (1.16.0 available)
| + convert 3.0.1
| + coverage 1.3.2
| + crypto 3.0.2
| + file 6.1.2
| + frontend_server_client 2.1.3
| + glob 2.0.2
| + http_multi_server 3.2.0
| + http_parser 4.0.1
| + io 1.0.3
| + js 0.6.4
| + lints 2.0.0
| + logging 1.0.2
| + matcher 0.12.11
| + meta 1.8.0
| + mime 1.0.2
| + node_preamble 2.0.1
| + package_config 2.0.2
| + path 1.8.2
| + pool 1.5.0
| + pub_semver 2.1.1
| + shelf 1.3.0
| + shelf_packages_handler 3.0.0
| + shelf_static 1.1.0
| + shelf_web_socket 1.0.1
| + source_map_stack_trace 2.1.0
| + source_maps 0.10.10
| + source_span 1.9.0
| + stack_trace 1.10.0
| + stream_channel 2.1.0
| + string_scanner 1.1.1
| + term_glyph 1.2.0
| + test 1.21.1
| + test_api 0.4.9
| + test_core 0.4.13
| + typed_data 1.3.1
| + vm_service 8.3.0
| + watcher 1.0.1
| + web_socket_channel 2.2.0
| + webkit_inspection_protocol 1.1.0
| + yaml 3.1.1
| Downloading collection 1.15.0...
| Downloading test 1.21.1...
| Downloading test_core 0.4.13...
| Downloading typed_data 1.3.1...
| Downloading string_scanner 1.1.1...
| Downloading http_parser 4.0.1...
| Downloading yaml 3.1.1...
| Downloading webkit_inspection_protocol 1.1.0...
| Downloading web_socket_channel 2.2.0...
| Downloading path 1.8.2...
| Downloading mime 1.0.2...
| Downloading crypto 3.0.2...
| Downloading source_span 1.9.0...
| Downloading frontend_server_client 2.1.3...
| Downloading shelf 1.3.0...
| Downloading analyzer 4.1.0...
| Downloading _fe_analyzer_shared 40.0.0...
| Downloading meta 1.8.0...
| Downloading args 2.3.1...
| Downloading async 2.9.0...
| Downloading coverage 1.3.2...
| Downloading vm_service 8.3.0...
| Changed 46 dependencies!
| + cat pubspec.yaml
| name: build
| description: A starting point for Dart libraries or applications.
| version: 1.0.0
| # homepage: https://www.example.com
|
| environment:
|   sdk: '>=2.17.1 <3.0.0'
|
| # dependencies:
| #   path: ^1.8.0
|
| dev_dependencies:
|   lints: ^2.0.0
|   test: ^1.16.0
| dependencies: {collection: 1.15.0}
| + dart pub add sprintf
| Resolving dependencies...
|   collection 1.15.0 (1.16.0 available)
| + sprintf 6.0.0
| Downloading sprintf 6.0.0...
| Changed 1 dependency!
| + dart pub add tuple
| Resolving dependencies...
|   collection 1.15.0 (1.16.0 available)
| + quiver 3.1.0
| + tuple 2.0.0
| Downloading tuple 2.0.0...
| Downloading quiver 3.1.0...
| Changed 2 dependencies!
| + cat pubspec.yaml
| name: build
| description: A starting point for Dart libraries or applications.
| version: 1.0.0
| # homepage: https://www.example.com
|
| environment:
|   sdk: '>=2.17.1 <3.0.0'
|
| # dependencies:
| #   path: ^1.8.0
|
| dev_dependencies:
|   lints: ^2.0.0
|   test: ^1.16.0
| dependencies: {collection: 1.15.0, sprintf: ^6.0.0, tuple: ^2.0.0}
| + sed -i.bak /test:/d pubspec.yaml
| + sed -i.bak s:1.16.0:1.15.0: pubspec.yaml
| + flutter pub add vnum
|
|   ╔════════════════════════════════════════════════════════════════════════════╗
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|
|
| Running "flutter pub get" in flutter_tools...                       6.8s
| Because every version of vnum depends on flutter from sdk which depends on collection 1.16.0, every version of vnum requires collection 1.16.0.
| So, because build depends on both collection 1.15.0 and vnum any, version solving failed.
```