orca: add versions 6.1.1 and avx2-6.1.1

[klartz]

Add the latest ORCA versions: 6.1.1 and avx2-6.1.1.

Issue #47489 discusses a change in ORCA’s filename scheme compared to earlier releases, and suggests treating avx2-6.0.1 as a temporary edge case until a later release clarified which scheme would be used going forward.
Based on the currently available releases, it seems that ORCA is continuing to use the avx2-6.0.1 filename scheme:

avx2-6.0.0    orca_6_0_0_linux_x86-64_avx2_shared_openmpi416.tar.xz
avx2-6.0.1    orca_6_0_1_linux_x86-64_shared_openmpi416_avx2.tar.xz
avx2-6.1.1    orca_6_1_1_linux_x86-64_shared_openmpi418_avx2.tar.xz

So I’ve also modified the URL construction logic to treat avx2-6.0.0 as the edge case instead, and to use the newer filename scheme for later versions.