fix: cast Core upload header values to strings#9208

GrahamCampbell wants to merge 1 commit into

googleapis:maingoogleapis/google-cloud-php:mainfrom

GrahamCampbell:fix/core-psr7-string-header-valuesGrahamCampbell/google-cloud-php:fix/core-psr7-string-header-valuesCopy head branch name to clipboard