I saw that this test is failing at head, with what turns out to be a
dependency on the test environment umask.

This removes the over-strict assertions about permissions from extracted
zips when permissions aren't preserved. I tested locally that it passes
with 022, 002, 077.

Also, some of the comments and variable names seemed to be out of date
for this test, in which the file is not executable, so I changed/removed
them.

cc @MrSubidubi 

follows on from #45515


Before:

```
mbp@amorfati ~/s/zed> umask 002
mbp@amorfati ~/s/zed> cargo nextest run -p util archive::tests::test_extract_zip_sets_default_permissions
    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.21s
────────────
 Nextest run ID de9e0712-0db1-4e4e-8c9f-421bb68ed23c with nextest profile: default
    Starting 1 test across 1 binary (71 tests skipped)
        FAIL [   0.003s] util archive::tests::test_extract_zip_sets_default_permissions
  stdout ───

    running 1 test
    test archive::tests::test_extract_zip_sets_default_permissions ... FAILED

    failures:

    failures:
        archive::tests::test_extract_zip_sets_default_permissions

    test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 71 filtered out; finished in 0.00s

  stderr ───

    thread 'archive::tests::test_extract_zip_sets_default_permissions' (755934) panicked at crates/util/src/archive.rs:290:13:
    assertion `left == right` failed: Expected default set of permissions for unzipped file with no permissions set.
      left: 436
     right: 420
    note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```


Closes #ISSUE

Release Notes:

- N/A