[mono] Don't crash when new unsupported intrinsic groups are added

[imhameed]

See #51998 (comment) and the following comments. #51998 (comment) should have been sufficient to allow Mono to execute the AvxVnni tests in this PR without crashing.

Relevant logs:
https://dev.azure.com/dnceng/public/_build/results?buildId=1148988&view=logs&jobId=e8cc9eb8-98f1-55f3-b6df-6c384ccb39b6&j=e8cc9eb8-98f1-55f3-b6df-6c384ccb39b6&t=7ec1aa02-369c-51d1-7a60-8e709c4509a9
https://dev.azure.com/dnceng/public/_build/results?buildId=1148988&view=logs&jobId=74e689b1-5e71-5f30-9486-7c2c5ff44021&j=74e689b1-5e71-5f30-9486-7c2c5ff44021&t=bc7664d5-2e7c-57dc-1337-ab0ada348ecf

[imhameed]

Should have been fixed by #53752; the AvxVnni tests will be reenabled by #54127.

[imhameed]

#54127 was merged. The AvxVnni tests are running successfully now.