Fall back to no authentication when OSS Index API token decryption fails

[nscuro]

Description

Adds a fallback to no authentication when OSS Index API token decryption fails.

Instead of causing a full-blown service disruption when API token decryption fails, fall back to unauthenticated API usage to limit the impact.

Addressed Issue

Relates to #2366

Additional Details

N/A

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have added corresponding update logic
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.03% (target: -1.00%)	✅ 95.83% (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (664ee25)	22054	16497	74.80%
Head commit (21af7b2)	22052 (-2)	16503 (+6)	74.84% (+0.03%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#3661)	24	23	95.83%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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