Running "pdm update --unconstrained --dry-run" will modufy pyproject.toml

[jmfederico]

• I have searched the issue tracker and believe that this is not a duplicate.

Make sure you run commands with -v flag before pasting the output.

Steps to reproduce

pdm init
pdm add --save-compatible boto3
pdm update --unconstrained --dry-run

Actual behavior

Version specifier for boto3 is changed in pyproject.toml to >=.

Expected behavior

No changes should have been made to pyproject.toml, version specifier for boto3 should be kept as ~=.

Environment Information

PDM version:
  2.8.0
Python Interpreter:
  /Volumes/Utveckling/testpdm/.venv/bin/python (3.9)
Project Root:
  /Volumes/Utveckling/testpdm
Local Packages:

{
  "implementation_name": "cpython",
  "implementation_version": "3.9.6",
  "os_name": "posix",
  "platform_machine": "arm64",
  "platform_release": "22.5.0",
  "platform_system": "Darwin",
  "platform_version": "Darwin Kernel Version 22.5.0: Thu Jun  8 22:22:20 PDT
2023; root:xnu-8796.121.3~7/RELEASE_ARM64_T6000",
  "python_full_version": "3.9.6",
  "platform_python_implementation": "CPython",
  "python_version": "3.9",
  "sys_platform": "darwin"
}