ci: treat test-infra modules as testable for -amd expansion

When a test-infra module changes (e.g., container version bump), its
dependents should be tested via -amd even though the test-infra module
itself has no src/test. Previously these were classified as "pom-only"
and excluded from -amd expansion, so component tests were never run.

Fixes the issue seen in PR apache#22316 where bumping the Infinispan container
version didn't trigger camel-infinispan tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: gnodet

.github/actions/incremental-build/incremental-build.sh

@@ -556,6 +556,11 @@ main() {
   for w in $(echo "$pl" | tr ',' '\n'); do
     if [ -d "$w/src/test" ]; then
       testable_pl="${testable_pl:+${testable_pl},}${w}"
+    elif [[ "$w" == test-infra/* ]]; then
+      # test-infra modules have no tests themselves but their dependents do —
+      # treat them as testable so -amd expands to the components that use them
+      testable_pl="${testable_pl:+${testable_pl},}${w}"
+      echo "  Test-infra module (no src/test, but dependents will be tested via -amd): $w"
     else
       pom_only_pl="${pom_only_pl:+${pom_only_pl},}${w}"
       echo "  Pom-only module (no src/test, won't expand dependents): $w"