check_postgres: install correctly on Big Sur
check_postgres: install correctly on Big Sur

As discussed with https://github.com/Homebrew/homebrew-core/pull/66370#issuecomment-740856994
Big Sur's system perl changed how "PREFIX=" is treated as an install
destination.  The more explicit way to control MakeMaker is to set
INSTALL_BASE instead, which should result in consistent behavior
between different OS/X versions.

Closes #67819.

Signed-off-by: chenrui <5fd29470147430022ff146db88de16ee91dea376@gmail.com>

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