Add "CGO_ENABLED=0" to build and release workflow

[notxarb]

This addresses a bug when trying to use the current release on alpine linux on x86-64.
While debugging an issue with using the release on alpine linux I ran the ldd command:

ldd /usr/local/bin/clair-scanner 
	/lib64/ld-linux-x86-64.so.2 (0x773b6b9a7000)
	libc.so.6 => /lib64/ld-linux-x86-64.so.2 (0x773b6b9a7000)
Error relocating /usr/local/bin/clair-scanner: __vfprintf_chk: symbol not found
Error relocating /usr/local/bin/clair-scanner: __fprintf_chk: symbol not found

I did not see the issue with the arm64 version. Probably because it is cross compiled, and will does static linking instead
ldd output from the arm64 file:

ldd /usr/local/bin/clair-scanner 
/lib/ld-musl-aarch64.so.1: /usr/local/bin/clair-scanner: Not a valid dynamic program

Adding the CGO_ENABLED=0 to the build command should force it to do a static build and fix it for alpine linux users.
The Makefile passes the CGO_ENABLED=0 when building.

Downloading from the build from my fork results in what I would expect:

curl -SLo /usr/local/bin/clair-scanner https://github.com/notxarb/clair-scanner/releases/download/alpine-com
pat/clair-scanner_linux-amd64
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
100 12.4M  100 12.4M    0     0  7180k      0  0:00:01  0:00:01 --:--:-- 13.1M
ldd /usr/local/bin/clair-scanner
/lib/ld-musl-x86_64.so.1: /usr/local/bin/clair-scanner: Not a valid dynamic program