Fix compiled name of DBT_ENV_CUSTOM_ENV_MY_FAVORITE_NUMBER

[adrian-pasek-prv]

What are you changing in this pull request and why?

DBT_ENV_CUSTOM_ENV_MY_FAVORITE_NUMBER should be compiled as MY_FAVORITE_NUMBER as per documentation:
Any env var named with the prefix DBT_ENV_CUSTOM_ENV_ will be included in two places, with its prefix-stripped name as the key:

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