<snip>

update-initramfs: Generating /boot/initrd.img-5.12.0-rc3-GIDI_DEV+
dpkg: warning: version '5.12.0-rc3-GIDI_DEV+' has bad syntax: invalid character in revision number
dpkg: warning: version '5.12.0-rc3-GIDI_DEV+' has bad syntax: invalid character in revision number

<snip>

This is a standard warning, arising because the version contains an underscore, which is against Debian Policy.
Remove the underscore and retry :-)

Try CONFIG_LOCALVERSION="-GIDI-DEV"

Good luck - Aruna