fix: ship shared capa test fixtures in the wheel

MANIFEST.in already declares that the three shared capa fixtures --
``response_xml_factory``, ``helpers`` and ``test_util`` -- must stay in the
distribution because openedx-platform imports them from its own test suite:

    # --- TEST UTILITY INCLUSIONS ---
    # Re-include specific test files that are excluded above.
    # We do this because openedx-platform imports these specific test helpers.
    include xblocks_contrib/problem/capa/tests/test_util.py
    include xblocks_contrib/problem/capa/tests/helpers.py
    include xblocks_contrib/problem/capa/tests/response_xml_factory.py

MANIFEST.in only governs the sdist though. Wheel contents come from
``[tool.setuptools.packages.find]``, whose blanket ``*tests*`` exclusion drops
the whole ``xblocks_contrib.problem.capa.tests`` package, so the intent above
has not applied to the wheel since 1.0.0.

Consequence: any openedx-platform version installing xblocks-contrib >=1.0.0
fails to collect ~17 of its own test modules with

    ModuleNotFoundError: No module named 'xblocks_contrib.problem.capa.tests'

which is why openedx-platform is pinned back to 0.17.0 and cannot pick up
newer releases.

Spell the exclusions out per package instead of using a blanket glob, so the
capa fixtures stay discoverable. Verified by building the wheel: the capa
tests package is present, no other test package is, and the uncompressed size
grows 5.07MB -> 5.54MB.

Author: AhtishamShahid

pyproject.toml

@@ -127,10 +127,32 @@ include-package-data = true
 
 [tool.setuptools.packages.find]
 include = ["xblocks_contrib*", "xblock_pdf*"]
-exclude = ["*tests*"]
+# Test packages are not shipped, with one deliberate exception:
+# ``xblocks_contrib.problem.capa.tests`` holds shared capa fixtures
+# (``response_xml_factory``, ``helpers``, ``test_util``) that openedx-platform
+# imports from ~17 of its own test modules. MANIFEST.in already declares that
+# intent, but it only governs the sdist -- wheel contents come from the package
+# discovery below, so this package must stay discoverable. The exclusions are
+# therefore listed per package rather than as a blanket ``*tests*``.
+exclude = [
+    "xblock_pdf.tests*",
+    "xblock_pdf.js_tests*",
+    "xblocks_contrib.annotatable.tests*",
+    "xblocks_contrib.discussion.tests*",
+    "xblocks_contrib.html.tests*",
+    "xblocks_contrib.lti.tests*",
+    "xblocks_contrib.poll.tests*",
+    "xblocks_contrib.problem.tests*",
+    "xblocks_contrib.problem.capa.safe_exec.tests*",
+    "xblocks_contrib.video.tests*",
+    "xblocks_contrib.word_cloud.tests*",
+]
 
 [tool.setuptools.exclude-package-data]
 "*" = ["tests*", "*.tests*", "spec*", "*.spec*"]
+# The capa fixtures ship as Python modules of the package above, which this
+# setting does not affect. Its problem-XML corpus is package data, and stays out.
+"xblocks_contrib.problem.capa.tests" = ["test_files*"]
 
 [tool.edx_lint]
 uv_constraints = [