Bug: 'python latest' tries to install stackless-3.7.5 on the unreleased version

[XaF]

[1/5] ✖ python (latest): error: execution error: ASDF_DATA_DIR="/Users/xaf/.local/share/omni/asdf" ASDF_DIR="/Users/xaf/.local/share/omni/asdf" "/Users/xaf/.local/share/omni/asdf/bin/asdf" "install" "python" "stackless-3.7.5"
omni: up command failed: issue while setting repo up: execution error: ASDF_DATA_DIR="/Users/xaf/.local/share/omni/asdf" ASDF_DIR="/Users/xaf/.local/share/omni/asdf" "/Users/xaf/.local/share/omni/asdf/bin/asdf" "install" "python" "stackless-3.7.5"

Seems that some of the new logic for handling asdf tools versions is picking up stackless-3.7.5 as a valid version number for latest. This is normal as the new logic validates all values when using latest, whereas we would want to at least check that the value only contains numbers and dots, starting with a number.