chore(ci): Pin Java 17 for lowest-direct cell

PySpark 3.4 (the declared floor) doesn't run on Java 21, the default
JDK on ubuntu-latest runners -- it hits NoSuchMethodException on
java.nio.DirectByteBuffer.<init>(long, int), removed in JDK 21. Pin
the lowest-direct cell to Java 17 so the resolved pyspark==3.4.0 can
actually start. The default cell (which resolves to a current pyspark
4.x) keeps the runner's default Java 21.

Signed-off-by: Seth Fitzsimmons <seth@mojodna.net>

Author: sethfitz

.github/workflows/check-python-code.yaml

@@ -31,7 +31,8 @@ jobs:
         # Default resolution exercises the committed lock against every
         # supported Python minor version. The lowest-direct cell pins each
         # direct dependency to its declared floor (see UV_RESOLUTION below)
-        # and runs only on the Python floor.
+        # and runs only on the Python floor, since the resolved-low pyspark
+        # 3.4 wheels exist for 3.10/3.11 only.
         python: ["3.10", "3.11", "3.12", "3.13", "3.14"]
         resolution: [default]
         include:
@@ -56,9 +57,19 @@ jobs:
         with:
           python-version: ${{ matrix.python }}
 
+      # PySpark 3.4 (the declared minimum) does not support Java 21, which is
+      # the default JDK on ubuntu-latest runners. Pin to Java 17 for the
+      # lowest-direct cell so the resolved pyspark==3.4.0 can actually start.
+      - name: Set up JDK 17
+        if: matrix.resolution == 'lowest-direct'
+        uses: actions/setup-java@be666c2fcd27ec809703dec50e508c2fdc7f6654 # v5.2.0
+        with:
+          distribution: temurin
+          java-version: '17'
+
       # UV_RESOLUTION=lowest-direct makes `uv sync` re-resolve every direct
       # dependency to the lowest version permitted by pyproject.toml. This
-      # exercises the declared floor (e.g. pydantic==2.12.0) instead of
+      # exercises the declared floor (e.g. pyspark==3.4.0) instead of
       # whatever the committed lock happens to point at. Failures here mean
       # a direct dep's minimum needs to be bumped. Set via GITHUB_ENV only
       # in the relevant cell so default cells run with no UV_RESOLUTION at