[BUG] `pyproject.toml`: Unicode character in a license file prevents dependencies from being installed

Description

Some licenses, in this specific example, LGPL-2.1, contains Unicode characters. In case of LGPL 2.1 it is U+000c - Form Feed character.

In pyproject.toml having a license file with those characters silently breaks package dependencies installation.

Expected behavior

• pip install -e . installs package dependencies
• pip install -e .[dev] installs optional dev dependencies group

pip version

23.2.1

Python version

3.10, 3.11

OS

Fedora Linux 38

How to Reproduce

1. Create pyproject.toml

[project]
name = "unicode-bug"
version = "0.1.0"
requires-python = ">=3.10"
license = {file = "LICENSE"}
dependencies = [
    "requests"
]
[project.optional-dependencies]
dev = [
  "pytest"
]

2. Create LICENSE file with unicode character

$ echo -e '\U000b' > LICENSE

3. Try to install the package and optional dependencies - doesn't install dependencies

$ pip install -e .
...
Successfully built unicode-bug
Installing collected packages: unicode-bug
  Attempting uninstall: unicode-bug
    Found existing installation: unicode-bug 0.1.0
    Uninstalling unicode-bug-0.1.0:
      Successfully uninstalled unicode-bug-0.1.0
Successfully installed unicode-bug-0.1.0

$ pip install -e .[dev]
...
WARNING: unicode-bug 0.1.0 does not provide the extra 'dev'
...

4. Remove unicode character

$ echo "" > LICENSE

3. Try to install the package and optional dependencies - installation works

$ pip install -e .
...
Successfully built unicode-bug
Installing collected packages: urllib3, idna, charset-normalizer, certifi, requests, unicode-bug
  Attempting uninstall: unicode-bug
    Found existing installation: unicode-bug 0.1.0
    Uninstalling unicode-bug-0.1.0:
      Successfully uninstalled unicode-bug-0.1.0
Successfully installed certifi-2023.7.22 charset-normalizer-3.2.0 idna-3.4 requests-2.31.0 unicode-bug-0.1.0 urllib3-2.0.4

$ pip install -e .[dev]
Successfully built unicode-bug
Installing collected packages: pluggy, packaging, iniconfig, unicode-bug, pytest
  Attempting uninstall: unicode-bug
    Found existing installation: unicode-bug 0.1.0
    Uninstalling unicode-bug-0.1.0:
      Successfully uninstalled unicode-bug-0.1.0
Successfully installed iniconfig-2.0.0 packaging-23.1 pluggy-1.3.0 pytest-7.4.0 unicode-bug-0.1.0

Output

No response

Code of Conduct

• I agree to follow the PSF Code of Conduct.

Start with the minimal pyproject.toml and LICENSE reproduction, comparing a form-feed character with an empty license file. Trace how setuptools handles license = {file = "LICENSE"} and the generated project metadata. Done means both pip install -e . and pip install -e .[dev] install requests and pytest without the missing-extra warning.