${_pkgbase}_git${_pkgsnap} is not considered a valid pkgver by pmbootstrap

… which unfortunately is the pkgver used by gcc at the moment: https://gitlab.alpinelinux.org/alpine/aports/-/blob/952225c9b9e70018154db1fcf27f8b7bd70bab63/main/gcc/APKBUILD#L7

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