glab: fix non-bash shell completion
glab: fix non-bash shell completion

Because `glab` expects the `-s`/`--shell` option, the formula
mistakenly installed the same bash completion for both zsh and fish
as well.

Revision bump to "push" fix to users.

Finally, I simplified the code a bit because AFAICT the current method
of manipulating the `SHELL` environment variable is either vestigial
or it actually never had the intended effect.

Closes #71766.

Co-authored-by: Rylan Polster <047d2ca1b3c34ce9eb9510507a88377ec1f9cce9@gmail.com>
Signed-off-by: Rylan Polster <047d2ca1b3c34ce9eb9510507a88377ec1f9cce9@gmail.com>
Signed-off-by: BrewTestBot <8a898ee6867e4f2028e63d2a6319b2224641c06c@users.noreply.github.com>

adam-moss/homebrew-core,mfikes/homebrew-core,nandub/homebrew-core,adam-moss/homebrew-core,JCount/homebrew-core,sjackman/homebrew-core,cblecker/homebrew-core,mbcoguno/homebrew-core,Homebrew/homebrew-core,nbari/homebrew-core,lemzwerg/homebrew-core,Linuxbrew/homebrew-core,mbcoguno/homebrew-core,stgraber/homebrew-core,nandub/homebrew-core,lemzwerg/homebrew-core,mfikes/homebrew-core,makigumo/homebrew-core,cblecker/homebrew-core,chrisfinazzo/homebrew-core,uyjulian/homebrew-core,stgraber/homebrew-core,filcab/homebrew-core,sjackman/homebrew-core,chrisfinazzo/homebrew-core,Homebrew/homebrew-core,zyedidia/homebrew-core,JCount/homebrew-core,Moisan/homebrew-core,nbari/homebrew-core,filcab/homebrew-core,Moisan/homebrew-core,makigumo/homebrew-core,uyjulian/homebrew-core,zyedidia/homebrew-core,mbcoguno/homebrew-core,Linuxbrew/homebrew-core