fix net10 build: comparison with string and int that worked until now

[helpimnotdrowning]

Description of the Change

Building on net10 failed because the build script tried comparing the major version "10" (a string) with 9 (an integer). I haven't checked how string/int comparisons work exactly, but "9" -ge 9 is True, but "10" -ge 9 is False. The script would wrongly find that net10 isn't able to build for any version of the framework and fail.

This patch just converts it to an integer.

Using:

• Debian 13, amd64
• dotnet 10.0.100 (via MS apt repo)

[Badgerati]

Spotted this issue myself while working on #1638 and fixed it there, I did it slightly differently though as I simplified the logic to just use dotnet --version - that's basically what the original logic boiled down to anyway.