TEST: Extend the kvstore test time out to 120s

[jamesbeyond]

Summary of changes

Extend the kvstore test time out to 120s, due to this test might take longer time to run on larger size SD card

Impact of changes

Migration actions required

Documentation

Not needed

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Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[x] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

@adbridge

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[ciarmcom]

@jamesbeyond, thank you for your changes.
@adbridge @ARMmbed/mbed-os-maintainers please review.

[adbridge]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 5 of 5 test jobs passed
Build number : 2
Build artifacts

[mbed-ci]

Test run: SUCCESS

Summary: 5 of 5 test jobs passed
Build number : 1
Build artifacts