Adopt the correct plural of "formula"

*Formulae* is the plural of *formula* only in the mathematical sense. But the theme of homebrew is beer, and the plural of a beer formula (i.e. a recipe) is *formulas*. Check the dictionary (alas, you have to do so manually, since GitHub eats the `dict://formula` link). It is true.

I have known this for a long time, but the recent example of issue #17381, and the renewed enthusiasm for the beer theme displayed in the beer emoji patch discussion, have finally pushed me to action.

This patch corrects the mistake by replacing occurrences of "formulae" with "formulas". I did not run a mass search-and-replace: I ran a mass search and quickly but manually checked each result. At first it might seem that only user-facing strings would need to be corrected, but leaving occurrences of "formulae" in internal names would only engender confusion in the contributors. To be effective, the correction has to be thorough.

If you were aware of this language subtlety, you will feel relieved. If you were not, you might feel incredulous for a moment, but you should quickly assimilate the correct usage. The truth shall set you free.