fix: Bump the Tutor version dependency to >=16.1.4

We rely on the Tutor OPENEDX_COMMON_VERSION variable to determine
the tag (or branch) to fetch for the Tubular repository.

In Tutor 16.1.4, the default value for OPENEDX_COMMON_VERSION changed
from open-release/palm.2 to open-release/palm.3. This means we now
need a version bump in our own install_requires list, so that we
require Tutor>=16.1.4.

Since this breaks compatibility with Open edX Olive (and will thus
require a major release bump on our part), update the README
accordingly.

Reference:
overhangio/tutor#923

CHANGELOG.md

@@ -1,3 +1,8 @@
+## Unreleased
+
+* [Enhancement] Support the Open edX `palm.3` release. Drop
+  compatibility with Open edX Olive.
+
 ## Version 2.1.0 (2023-08-23)
 
 * [Enhancement] Support Tutor 16 and Open edX Palm, Python 3.10, and Python 3.11.

README.md

@@ -19,7 +19,7 @@ appropriate one:
 | Maple            | `>=13.2, <14`[^1] | `maple`       | 0.1.x          |
 | Nutmeg           | `>=14.0, <15`     | `nutmeg`      | 1.x.x          |
 | Olive            | `>=15.0, <16`     | `main`        | 2.x.x          |
-| Palm             | `>=16.0, <17`     | `main`        | 2.x.x          |
+| Palm             | `>=16.0, <17`     | `main`        | 3.x.x          |
 
 [^1]: For Open edX Maple and Tutor 13, you must run version 13.2.0 or
    later. That is because this plugin uses the Tutor v1 plugin API,

setup.py

@@ -26,7 +26,7 @@ def load_readme():
     packages=find_packages(exclude=["tests*"]),
     include_package_data=True,
     python_requires=">=3.8",
-    install_requires=["tutor <17, >=15.0.0"],
+    install_requires=["tutor <17, >=16.1.4"],
     setup_requires=["setuptools-scm"],
     entry_points={
         "tutor.plugin.v1": [