You can use zlib-flate, like this:
cat .git/objects/c0/fb67ab3fda7909000da003f4b2ce50a53f43e7 \
| zlib-flate -uncompress; echo
It's there by default on my machine, but it's part of qpdf - tools for and transforming and inspecting PDF files
if you need to install it.
I've popped an echo
on the end of the command, as it's easier to read the output that way.