Fix build.sh break by poorly timed dotnet first time experience (#12727)

Fix build.sh break by poorly timed dotnet first time experience (#12727)

Depending on machine state, calling `dotnet` to dump the PGO and IBC
package version might trigger the first time experience message. This
breaks build.sh where it tries to parse the package version from `dotnet
msbuild`'s output. The fix is to disable the first time experience path
in these two invocations of `dotnet`.