fix: correct label mapping for collection metrics

[d0ugal]

Fix label mapping mismatch where collection metrics expected 'repo'
label but were receiving 'name' label. This was causing panics:

panic: label name "repo" missing in label map

The metrics definitions in ghcr_registry.go specify:

• CollectionFailedCounter: []string{"repo", "interval"}
• CollectionSuccessCounter: []string{"repo", "interval"}
• CollectionIntervalGauge: []string{"repo", "interval"}
• CollectionDurationGauge: []string{"repo", "interval"}
• CollectionTimestampGauge: []string{"repo", "interval"}

But the collector was using 'name' instead of 'repo' in the labels.

This highlights the need for better integration tests that would
catch label mapping mismatches before deployment.

Changes

• Fixed all collection metric label mappings from "name" to "repo"
• Maintained existing functionality while ensuring correct label names

Testing

• Build tested successfully
• Ready for deployment testing