fix: pin adlfs for azure public ingest regression (#4333)

adlfs changed in 2026.4.0 with a breaking auth change: the default anon
behavior flipped to False, so code that previously hit public Azure
blobs anonymously now tries DefaultAzureCredential unless anon=True is
set explicitly. that matches the CI failure here.

this pins `adlfs==2026.2.0` to temporarily unblock failing changes when
bumping to latest

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Pins `adlfs` to an older version to work around an Azure
public-container ingest regression, which can affect Azure connector
behavior at runtime. The rest is CI-only fixture update plumbing and is
low risk.
> 
> **Overview**
> Pins `adlfs` to `==2026.2.0` via `pyproject.toml` UV constraints (and
updates `uv.lock`) to avoid a regression affecting anonymous access to
public Azure blob containers.
> 
> Updates the `ingest-test-fixtures-update-pr` GitHub Actions workflow
to also generate and include `expected-structured-output-markdown`
fixtures in the auto-created PRs, and records this change in the
`CHANGELOG.md`.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
88a7801. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Vladimir Kirilenko <vladimir.kirilenko@deepsense.ai>

Author: ryannikolaidis

pyproject.toml

@@ -196,6 +196,8 @@ required-environments = [
     "sys_platform == 'win32'",
 ]
 constraint-dependencies = [
+    # Temporary pin for Azure public-container ingest regression in adlfs 2026.4.0 stack
+    "adlfs==2026.2.0",
     # deltalake 1.3.0 is missing Linux ARM64 wheels, causing Docker ARM64 builds to fail
     "deltalake<1.3.0",
     "fonttools>=4.60.2",