Update cosign image in validate-release job

[priyawadhwa]

CI is failing in #921 because of a bug in cosign 1.8.0 which was fixed in 1.9.0 (sigstore/cosign#1992)

Signed-off-by: Priya Wadhwa [email protected]

Summary

Release Note

Documentation

[codecov-commenter]

Codecov Report

Merging #931 (ec0b22e) into main (fd0d500) will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #931      +/-   ##
==========================================
- Coverage   48.22%   48.16%   -0.06%     
==========================================
  Files          62       62              
  Lines        5398     5398              
==========================================
- Hits         2603     2600       -3     
- Misses       2513     2515       +2     
- Partials      282      283       +1     

Impacted Files	Coverage Δ
pkg/types/alpine/v0.0.1/entry.go	55.46% <0.00%> (-1.27%)	⬇️

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