[release/6.0] Fix GENERIC_MATH_FEATURE by making sure we always choose the right ref

[safern]

Fixes: #62840

Customer Impact

With the current file version approach, every servicing release we produce of the ref assembly pack will cause System.Runtime.dll to have a higher file version than the one we ship in System.Runtime.Experimental package, causing assembly conflict resolution to prefer the ref assembly that ships inbox as part of the targeting pack, causing compile errors to users when upgrade to a new SDK like:

error CS0246: The type or namespace name 'IComparisonOperators<,>' could not be found (are you missing a using directive or an assembly reference?

By upgrading the min version of the file version we ensure that it is always greater as now the file version for the experimental one will be 6.100.x.x vs the one inbox will be 6.0.x.x

Testing

I tested with the sample repro by referencing a new package produced locally with the fix and the compiler errors go away. Also visually validated via a binlog that the right System.Runtime.dll is chosen as a reference when compiling.

Risk

Low, we are just changing the assembly file version scheme to make sure it is always greater for the current SDK band.

[ghost]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[safern]

Failures are linked and known. Change approved offline.

[ericstj]

LGTM, thanks for picking this up, @safern