perf: improve release validation performance

[letFunny]

Avoid expensive calls to look for conflicts when the prefixes do not
match.

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I tried many performance improvements and rewrites of the logic below. This are the only ones that move the needle significantly. With big rewrites of the algorithm I am able to get a ~6% more, so in my opinion it is not worth going that route of extra complexity and longer reviews; we should look for performance improvements elsewhere. I also tried many other tricks like finding the end index by using binary search as well, being more clever about the prefix, etc. and none of them increased performance more than 2/3% compared to this PR, so again they were not included as they made the code more complex.

[letFunny]

The comment is not posted, I have downloaded the numbers from the CI artifacts:

| Command | Mean [s] | Min [s] | Max [s] | Relative |
|:---|---:|---:|---:|---:|
| `BASE` | 13.901 ± 0.136 | 13.709 | 14.233 | 3.11 ± 0.07 |
| `HEAD` | 4.477 ± 0.087 | 4.391 | 4.619 | 1.00 |

So a 3x improvement.