tests/functional2: fix non-working failsafe and resulting warning

Silly me forgot to add the dependency responsible for handling
`@pytest.mark.timeout` failsafes to kill a test if it takes too long,
which results in a warning when running f2.
This commit adds the required dependency and hence removes the warning

Change-Id: I281cad05bb0cf50208f72080cb2bfd8cbfb09d0c

package.nix

@@ -243,6 +243,7 @@ stdenv.mkDerivation (finalAttrs: {
     ++ lib.optionals finalAttrs.doCheck [
       (dontWrapPython p.pytest)
       p.pytest-xdist
+      p.pytest-timeout
       p.ruff
       p.aiohttp
     ]
@@ -573,6 +574,7 @@ stdenv.mkDerivation (finalAttrs: {
             # wrapped python instead of build inputs for its python inputs
             (dontWrapPython p.pytest)
             p.pytest-xdist
+            p.pytest-timeout
             p.ruff
             p.aiohttp
             p.python-frontmatter