Fix a bug where no warning is output when parsing of workspace settings fails. (#4014)
## Summary
See #4013
`uv pip ...` command loads workspace settings from pyproject.toml and
uv.toml.
Although a warning is implemented to output a warning when parsing
fails, it is not actually output.
https://github.com/astral-sh/uv/blob/main/crates/uv-workspace/src/workspace.rs#L38-L61
The reason is that the flag to display warnings is enabled after loading
the workspace settings.
This PR turns on the warning output flag before loading the workspace.
## Test Plan
pyproject.toml for test
```toml
[project]
name = "sample"
version = "0.0.0"
dependencies = ["ruff"]
[tool.uv.pip]
# originally string type.
index-url = 1
```
command output (before modification)
```bash
uv pip compile pyproject.toml
Resolved 1 package in 383ms
# This file was autogenerated by uv via the following command:
# uv pip compile pyproject.toml
ruff==0.4.7
# via sample (pyproject.toml)
```
command output (after modification)
```bash
uv pip compile pyproject.toml
warning: Failed to parse `pyproject.toml`: TOML parse error at line 7, column 13
|
7 | index-url = true
| ^^^^
invalid type: boolean `true`, expected a string
Resolved 1 package in 107ms
# This file was autogenerated by uv via the following command:
# uv pip compile pyproject.toml
ruff==0.4.7
# via sample (pyproject.toml)
```