fix(ci): prevent matrix-generation steps from masking gradle failures

The dynamic matrix steps (find_gradle_jobs, find_examples_jobs,
find_docs_examples_jobs) captured `./gradlew testMatrix` output inside a
command substitution, in two cases piped into jq. In a pipeline the step
exit status is that of the last command (jq), so a gradle failure (e.g. a
module that does not compile) was masked: jq exits 0 on empty input, the
step reported success, and an empty/invalid matrix was emitted.

An empty matrix means GitHub spawns zero `check` jobs, and since the
downstream jobs are chained via `needs:`
(check -> find_examples_jobs -> check_examples -> find_docs_examples_jobs
-> check_docs_examples), they all get skipped. The net effect is a
falsely-green build that ran no module checks at all. This recently let a
breaking dependency bump (cassandra-driver-core 4.0.0) pass CI as green.

Fix: add `set -o pipefail` and run gradle on its own line, redirecting
output to a file before handing it to jq. Gradle's non-zero exit is now
caught directly by the default `set -e`, before the matrix output is
written.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: kiview

.github/workflows/ci.yml

@@ -96,7 +96,9 @@ jobs:
           # we should not push empty results to the cache
           READ_ONLY_REMOTE_GRADLE_CACHE: true
         run: |
-          TASKS=$(./gradlew --no-daemon --parallel -q testMatrix | jq 'del(.[] | select(. == ":testcontainers:check" or startswith(":docs:")))' --compact-output)
+          set -o pipefail
+          ./gradlew --no-daemon --parallel -q testMatrix > matrix.json
+          TASKS=$(jq 'del(.[] | select(. == ":testcontainers:check" or startswith(":docs:")))' --compact-output matrix.json)
           echo $TASKS
           echo "matrix={\"gradle_args\":$TASKS}" >> $GITHUB_OUTPUT
   check:
@@ -130,7 +132,9 @@ jobs:
           # we should not push empty results to the cache
           READ_ONLY_REMOTE_GRADLE_CACHE: true
         run: |
-          TASKS=$(./gradlew --no-daemon --parallel -q testMatrix)
+          set -o pipefail
+          ./gradlew --no-daemon --parallel -q testMatrix > matrix.json
+          TASKS=$(cat matrix.json)
           echo $TASKS
           echo "matrix={\"gradle_args\":$TASKS}" >> $GITHUB_OUTPUT
   check_examples:
@@ -164,7 +168,9 @@ jobs:
           # we should not push empty results to the cache
           READ_ONLY_REMOTE_GRADLE_CACHE: true
         run: |
-          TASKS=$(./gradlew --no-daemon --parallel -q testMatrix | jq 'map(select(startswith(":docs:")))' --compact-output)
+          set -o pipefail
+          ./gradlew --no-daemon --parallel -q testMatrix > matrix.json
+          TASKS=$(jq 'map(select(startswith(":docs:")))' --compact-output matrix.json)
           echo $TASKS
           echo "matrix={\"gradle_args\":$TASKS}" >> $GITHUB_OUTPUT
   check_docs_examples: