test_simple: fix accidentally skipped test

[woodruffw]

This moves _update_context below test_with_files_quarantined_omitted_from_index and into a proper indentation, unskipping test_with_files_quarantined_omitted_from_index in the progress. I'm a little surprised test_with_files_quarantined_omitted_from_index's skippage wasn't caught by any dead code/unreachability checks 🤔

To get test_with_files_quarantined_omitted_from_index passing, I cargo-culted changed based on the other test changes made in #15716.

CC @ewdurbin @cofiem

See #15716 (review)

[miketheman]

I'm a little surprised test_with_files_quarantined_omitted_from_index's skippage wasn't caught by any dead code/unreachability checks

We don't currently report on coverage of the tests/ folder, as that would fail our checks today - there's a bunch of LOC in the test/fixtures that don't get reported as covered.

Apply this diff and run make tests to see:

diff --git a/pyproject.toml b/pyproject.toml
index e44f6a68e..c07d3cbaf 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,7 +1,7 @@
 [tool.coverage.run]
 branch = true
 dynamic_context = "test_function"
-source = ["warehouse"]
+source = ["warehouse", "tests"]
 omit = [
   # We don't want to get coverage information for our migrations.
   "warehouse/migrations/*",

It's probably worth trying to burn down those instances, so we can apply this diff and ensure that every line of code in the tests/ folder gets executed during a test suite run.