fix: let warnaserror "false" disable -warnaserror

Even as a string input, act_runner delivers the value as
'%!t(string=false)', so an exact comparison never matches.
Match case-insensitively on the substring "false" instead.

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

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

@@ -18,7 +18,7 @@ on:
         required: false
         default: "Release"
         type: string
-      # string, not boolean: act_runner mangles boolean defaults (format() yields '%!t(string=false)').
+      # string, not boolean: act_runner mangles boolean defaults. The value may still arrive as '%!t(string=…)', see Build step.
       warnaserror:
         description: "Treat build warnings as errors (\"true\"/\"false\")"
         required: false
@@ -101,9 +101,11 @@ jobs:
       - name: Build
         run: |
           ARGS=(-c "$CONFIGURATION" --no-restore)
-          if [ "${WARNASERROR,,}" != "false" ]; then
-            ARGS+=(-warnaserror)
-          fi
+          # act_runner may deliver the value mangled as '%!t(string=false)', so match by substring.
+          case "${WARNASERROR,,}" in
+            *false*) ;;
+            *) ARGS+=(-warnaserror) ;;
+          esac
           set -x
           dotnet build ${SOLUTION:+"$SOLUTION"} "${ARGS[@]}"