Update requirements.txt

[Friedrich2]

The dependencies required by SBTi-finance-tool seem to be defined via requirements.txt.

These dependencies are pinned down to a specific version. Some of these are not the current versions.
For example, requirements.txt requires exactly pandas 1.5.3 and numpy 1.22.0, while the current versions of these two packages are pandas 2.1.4 and numpy 1.26.0.

I propose to use another form of requirement specifier specifying a half-closed interval (e. g. pandas >= 1.5.3). In this way, it is not needed to install multiple versions of the same package while using another package requesting the current version.

The issue arose during the use of for /F "skip=2 tokens=1" %a in ('pip list --outdated') do pip install --upgrade %a under Windows to upgrade all pip packages to the current version, implicitly hoping that every package works with the newest versions of its dependencies.