chore(deps): update actions/cache action to v2.1.8

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
actions/cache	action	patch	v2.1.2 -> v2.1.8

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Release Notes

actions/cache (actions/cache)

v2.1.8: Updating actions/core to version 1.10.0

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The ::save-state and ::set-output are deprecated. The newer version of actions/core >1.10.0 uses the new syntax for save and set output. After this change, customers using actions/cache@v2 won't see deprecation warning message.

v2.1.7

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Support 10GB cache upload using the latest version 1.0.8 of @actions/cache

v2.1.6

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• Catch unhandled "bad file descriptor" errors that sometimes occurs when the cache server returns non-successful response (https://github.com/actions/cache/pull/596)

v2.1.5

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• Fix permissions error seen when extracting caches with GNU tar that were previously created using BSD tar (https://github.com/actions/cache/issues/527)

v2.1.4

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• Make caching more verbose #​650
• Use GNU tar on macOS if available #​701

v2.1.3

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• Upgrades @actions/core to v1.2.6 for CVE-2020-15228. This action was not using the affected methods.
• Fix error handling in uploadChunk where 400-level errors were not being detected and handled correctly

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