💅 use ENV.fetch(name, default) form

[zzak]

Follow up to #47143, prefers the ENV.fetch(name, default) form instead of block form.

Block form is only useful if we want to yield the name, I think.

[ref]

[natematykiewicz]

Block form is also usually used when the default value is expensive to compute, since it only needs to be computed when the key doesn't exist. For static values, it's less code and faster to use 2 arguments and no block.

There's a Rubocop rule to prefer 2 arguments when the default is a simple static value.
rubocop/rubocop#8147

[zzak]

Good call @natematykiewicz, and thank you for explaining the differences to me.

I've opened #47327 to autocorrect any violations for that rule.