Ensure that `ActionController::Parameters` can still be passed to AR

Since nested hashes are also instances of
`ActionController::Parameters`, and we're explicitly looking to work
with a hash for nested attributes, this caused breakage in several
points.

This is the minimum viable fix for the issue (and one that I'm not
terribly fond of). I can't think of a better place to handle this at the
moment. I'd prefer to use some sort of solution that doesn't special
case AC::Parameters, but we can't use something like `to_h` or `to_a`
since `Enumerable` adds both.

While I've added a trivial test case for verifying this fix in
isolation, we really need better integration coverage to prevent
regressions like this in the future. We don't actually have a lot of
great places for integration coverage at the moment, so I'm deferring it
for now.

Fixes #20922.

1 files changed, 7 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 237b07f653..47364325ea 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   Ensure that `ActionController::Parameters` can still be passed to nested
+    attributes.
+
+    Fixes #20922.
+
+    *Sean Griffin*
+
 *   Deprecate force association reload by passing a truthy argument to
     association method.