refactor: drop Python 3.8 related code

[Molkree]

fixes #4579

tests and SBOM generation were already disabled in #4647
python_requires was already bumped in #5135

[Copilot]

Pull Request Overview

This PR removes Python 3.8 related code from the codebase after Python 3.8 support was officially dropped. The changes update version checks, modernize type annotations to use built-in collection types, and clean up version-specific conditional imports.

• Updated Python version checks from 3.8+ to 3.9+
• Replaced typing module imports with built-in collection types (dict, list, set)
• Removed conditional imports for older Python versions

Reviewed Changes

Copilot reviewed 21 out of 22 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/test_extractor.py	Updated test skip condition to remove Python 3.7 reference
test/language_data/requirements.txt	Removed Python 3.8 specific dependency and fixed typo
test/README.md	Updated documentation examples from Python 3.8/3.9 to 3.11/3.12
doc/MANUAL.md	Updated documentation to remove Python 3.8 reference
dev-requirements.txt	Consolidated development dependencies by removing Python version conditions
cve_bin_tool/vex_manager/parse.py	Modernized type annotations to use built-in types
cve_bin_tool/vex_manager/generate.py	Modernized type annotations to use built-in types
cve_bin_tool/version_scanner.py	Moved Iterator import from typing to collections.abc
cve_bin_tool/util.py	Modernized type annotations and moved imports
cve_bin_tool/strings.py	Modernized type annotations to use built-in types
cve_bin_tool/parsers/parse.py	Removed conditional import for importlib_resources
cve_bin_tool/package_list_parser.py	Modernized type annotations to use built-in types
cve_bin_tool/input_engine.py	Modernized type annotations and moved Iterable import
cve_bin_tool/helper_script.py	Moved MutableMapping import from typing to collections.abc
cve_bin_tool/data_sources/init.py	Removed conditional import for importlib_resources
cve_bin_tool/cve_scanner.py	Modernized type annotations to use built-in types
cve_bin_tool/csv2cve.py	Replaced inline version check with shared function
cve_bin_tool/config.py	Moved Mapping import from typing to collections.abc
cve_bin_tool/cli.py	Updated version check logic and extracted to reusable function
cve_bin_tool/checkers/init.py	Removed conditional import for importlib_resources
.pre-commit-config.yaml	Updated pyupgrade configuration from py38-plus to py39-plus

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