main/libcap: add missing makedepends
Bash is used to execute progs/mkcapshdoc.sh. When checks are disabled (e.g. for riscv64) those dependencies aren't installed either, and thus Bash was missing and it failed the build
Bash is used to execute progs/mkcapshdoc.sh. When checks are disabled (e.g. for riscv64) those dependencies aren't installed either, and thus Bash was missing and it failed the build