Auto merge of #2878 - Turbo87:num-format, r=jtgeibel
Auto merge of #2878 - Turbo87:num-format, r=jtgeibel

helpers/format-num: Fall back to `en` locale if `navigator.language` causes an error

This should resolve https://sentry.io/organizations/rust-lang/issues/1936687439/

r? `@jtgeibel`

rust-lang/crates.io,rust-lang/crates.io,rust-lang/crates.io,rust-lang/crates.io