fix flake in weighted random picker

[nirrozenbaum]

What type of PR is this?
/kind flake

What this PR does / why we need it:
Fix a test flake of random weighted picker.
This fix is based on expected probabilities with some tolerance to make sure the actual random sampling is close enough to the expected results. more on the numbers:

🔹 Setup

• Suppose expected probability = 𝑝.
• Number of trials = 𝑛 = 10000
• The observed count follows a binomial distribution:
  𝑋∼Binomial(𝑛,𝑝)
• Observed frequency = 𝑋/𝑛
• Standard deviation (σ) of observed frequency is:
  𝜎=sqrt(𝑝(1−𝑝)/𝑛)

🔹 Example: worst-case variance

The variance is largest at 𝑝=0.5

𝜎=sqrt(0.5⋅0.5/10000)≈0.005

So the natural “jitter” is about ±0.5 percentage points.

🔹 With tolerance = ±5% (0.05)

• Allowed range = expected ±0.05.
• That is 10× wider than σ.

In normal distribution terms, that’s a 10σ bound.
The probability of going beyond 10σ is about 10^-23 — practically impossible in the lifetime of the universe.

Which issue(s) this PR fixes:

Fixes #1538

Does this PR introduce a user-facing change?:

None

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nirrozenbaum

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[nirrozenbaum]

/cc @kfswain

[elevran]

I can't comment on the math (i.e., is the distribution of samples normal or binomial, should we be looking for actual P vs expected P to be within 5% based on the expected P or as absolute,...) but regarding the code:
/lgtm