fix: apply -warnaserror reliably

act_runner mangles boolean input defaults: format('{0}', inputs.warnaserror)
evaluated to '%!t(string=false)', so -warnaserror was never passed.
Input is now a string defaulting to "true"; anything but "false" enables it.
Build command is traced (set -x) so the log shows the flags used.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

.gitea/workflows/dotnet-build-test-postgres.yaml

@@ -18,11 +18,12 @@ on:
         required: false
         default: "Release"
         type: string
+      # string, not boolean: act_runner mangles boolean defaults (format() yields '%!t(string=false)').
       warnaserror:
-        description: "Treat build warnings as errors"
+        description: "Treat build warnings as errors (\"true\"/\"false\")"
         required: false
-        default: true
-        type: boolean
+        default: "true"
+        type: string
       working-directory:
         description: "Path where dotnet commands are executed (relative to repo root)"
         required: false
@@ -100,9 +101,10 @@ jobs:
       - name: Build
         run: |
           ARGS=(-c "$CONFIGURATION" --no-restore)
-          if [ "$WARNASERROR" = "true" ]; then
+          if [ "${WARNASERROR,,}" != "false" ]; then
             ARGS+=(-warnaserror)
           fi
+          set -x
           dotnet build ${SOLUTION:+"$SOLUTION"} "${ARGS[@]}"
 
       # The image's init phase listens on the unix socket only, so an open TCP port means the final server is up.