Fix flaky fuzz tests with count_values

[harry671003]

What this PR does:

• Fixes flakiness in fuzz tests for count_values func.
• count_values returns a float in the metric which is not always accurate.

[
  {
    "metric": { "job": "prometheus", "value": "0" },
    "value": [1734628158, "5"]
  },
  {
    "metric": { "job": "prometheus", "value": "16254.5" },
    "value": [1734628158, "9"]
  },
  {
    "metric": { "job": "prometheus", "value": "17551.083333333336" },
    "value": [1734628158, "1"]
  }
]

• Example of one such failure: https://github.com/cortexproject/cortex/actions/runs/12586943624/job/35081958645

Which issue(s) this PR fixes:
Fixes #

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[yeya24]

Thanks!