chore(conan): Avoid deprecated section name

[rettichschnidi]

This change is a preparation for Conan 2.x support in ORT.

With Conan 2, the section build_requires in conanfile.txt has been renamed to tool_requires. The old name is no longer supported and causes Conan (2.x) to fail with an error:

$ conan install conanfile.txt
...
ConfigParser: Unrecognized field 'build_requires'

Starting with Conan 1.44, tool_requires has been added to Conan 1.x as an alias for build_requires. Ever since, the official documentation does not mention a section named build_requires anymore.

Current 1.x docs: https://docs.conan.io/en/1.64/reference/conanfile_txt.html
Old 1.x docs: https://docs.conan.io/en/1.43/reference/conanfile_txt.html
Relevant issue: conan-io/conan#10168

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.79%. Comparing base (6f50cf5) to head (521150d).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8759   +/-   ##
=========================================
  Coverage     67.79%   67.79%           
  Complexity     1164     1164           
=========================================
  Files           243      243           
  Lines          7711     7711           
  Branches        861      861           
=========================================
  Hits           5228     5228           
  Misses         2127     2127           
  Partials        356      356           

Flag	Coverage Δ
funTest-docker	66.84% <ø> (ø)
funTest-non-docker	33.96% <ø> (ø)
test	38.12% <ø> (ø)

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[sschuberth]

I have no problems with raising the min. supported Conan version to 1.44.0, but we should double-check with the community, so I've added it to the agenda of today's call (which I cannot attend, however).

However, doing this as a preparation for Conan 2 support probably does not count, as over here we assumed that Conan 2 support would be implemented via a new independent package manager with its own test assets.

[sschuberth]

I've added it to the agenda of today's call (which I cannot attend, however).

I see that the community had no objections during the call, so let's move forward with this, even if not strictly required for Conan 2 support, which still could be implemented as a separate analyzer plugin.