Parsing issue in setup.cfg

### Description

> Parsing issue in setup.cfg

### How To Reproduce

```
[metadata]
name = build
version = 0.8.0
description = A simple, correct PEP 517 build frontend
long_description = file: README.md
long_description_content_type = text/markdown
author = Filipe Laíns
author_email = lains@riseup.net
license = MIT
license_file = LICENSE
classifiers =
License :: OSI Approved :: MIT License
Programming Language :: Python :: 3
Programming Language :: Python :: 3 :: Only
Programming Language :: Python :: 3.6
Programming Language :: Python :: 3.7
Programming Language :: Python :: 3.8
Programming Language :: Python :: 3.9
Programming Language :: Python :: 3.10
Programming Language :: Python :: Implementation :: CPython
Programming Language :: Python :: Implementation :: PyPy
project_urls =
homepage = https://github.com/pypa/build
changelog = https://pypa-build.readthedocs.io/en/stable/changelog.html

[options]
packages = find:
install_requires =
packaging>=19.0
pep517>=0.9.1
colorama;os_name == "nt" # not actually a runtime dependency, only supplied as there is not "recommended dependency" support
importlib-metadata>=0.22;python_version < "3.8"
tomli>=1.0.0;python_version < "3.11" # toml can be used instead -- in case it makes bootstrapping easier
python_requires = >=3.6
package_dir =
=src

[options.packages.find]
where = src

[options.entry_points]
console_scripts =
pyproject-build = build.__main__:entrypoint
pipx.run =
build = build.__main__:entrypoint

[options.extras_require]
docs =
furo>=2021.08.31
sphinx~=4.0
sphinx-argparse-cli>=1.5
sphinx-autodoc-typehints>=1.10
test =
filelock>=3
pytest>=6.2.4
pytest-cov>=2.12
pytest-mock>=2
pytest-rerunfailures>=9.1
pytest-xdist>=1.34
toml>=0.10.0
wheel>=0.36.0
setuptools>=42.0.0;python_version < "3.10"
setuptools>=56.0.0;python_version >= "3.10"
typing =
importlib-metadata>=4.6.4
mypy==0.950
typing-extensions>=3.7.4.3;python_version < "3.8"
virtualenv =
virtualenv>=20.0.35

[options.package_data]
build =
py.typed

[egg_info]
tag_build =
tag_date = 0
```
Parse this cfg file with `SetupCfgHandler`.

Expected : extracted_requirements should be like `packaging>=19.0`,
Computed: extracted_requirements is `>=19.0`

### System configuration

> For bug reports, it really helps us to know:

* What OS are you running on? Linux
* What version of scancode-toolkit was used to generate the scan file?
* What installation method was used to install/run scancode? source download