pip compile: change order of check to handle exact argument first

[skshetry]

I messed up the order of checks in #5033, due to which it failed to exclude the case of -P package, as arg.startswith("-P") check came first and skipped only the first argument.

That means that, in the following command:

uv pip compile --output-file pip_compile_uv_header.txt unpinned_uv.in -P attrs==18.1.0

The generated header would exclude -P, but keep attrs==18.1.0.

# This file was autogenerated by uv via the following command:
#    uv pip compile --output-file pip_compile_uv_header.txt unpinned_uv.in attrs==18.1.0

But we want to check for an exact match first and then only check for the case when option and value are together.

This also affected --find-links short option of style -f <uri>.

Hopefully, third times going to be a charm. 😳

Summary

Test Plan

I tested locally, and also changed one snapshot test to use -P for variation. I don't think it's worth an extra test, but can do that for sure.

[charliermarsh]

Thanks! I also missed this as reviewer, all good.

[avilaton]

I can feel the anxiety we all have to get this dependabot stuff merged, I coded most of that pr on my cellphone while doing other things.