save grype db cache on updates to avoid using stale cache db

[saisatishkarra]

• Fixes the issue to restore old cache when exists
• On DB drift, updates DB
• Save any DB updates back to same cache key and then use it

Issue:

Cache for main branch before PR is merged is stale (5 days old)

Error Saving cache with same key (when multiple jobs / parallel workflows are running at the same time)
Refer Workaround / Refer using-short-lived-caches

After PR is merged into main branch (Refer to action run after PR is merged for main branch):

[github-actions]

Luacheck Report

1 files  ±0  1 suites  ±0   0s ⏱️ ±0s
4 tests ±0  4 ✅ ±0  0 💤 ±0  0 ❌ ±0 
8 runs  ±0  8 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit fecaf6f. ± Comparison against base commit a213265.