fix: oci repo has no digest

[Abirdcfly]

Fix #252

$ helm pull oci://registry-1.docker.io/bitnamicharts/nginx --version 15.0.2
Pulled: registry-1.docker.io/bitnamicharts/nginx:15.0.2
Digest: sha256:32d95bdf27824295fcb8a9f7dd8e2b001524a9181d514076586f90565e986401

It is same with https://hub.docker.com/r/bitnamicharts/nginx/tags?page=1&name=15.0.2

we can use this digest for oci repo.

[codecov[bot]]

Codecov Report

Merging #291 (5a68ef9) into main (5b34475) will increase coverage by 0.12%. The diff coverage is 50.00%.

:exclamation: Current head 5a68ef9 differs from pull request most recent head ad33e57. Consider uploading reports for the commit ad33e57 to get more accurate results

@@            Coverage Diff             @@
##             main     #291      +/-   ##
==========================================
+ Coverage   15.68%   15.80%   +0.12%     
==========================================
  Files          36       36              
  Lines        3998     4004       +6     
==========================================
+ Hits          627      633       +6     
  Misses       3334     3334              
  Partials       37       37              

Files Changed	Coverage Δ
pkg/helm/helm.go	6.80% <50.00%> (+1.68%)	:arrow_up:

:mega: We’re building smart automated test selection to slash your CI/CD build times. Learn more