Use standard error format (#154)

Author: wmdietl

.github/workflows/build.yml

@@ -30,11 +30,11 @@ jobs:
         run: ./gradlew build conformanceTests demoTest --include-build ../jspecify
         env:
           SHALLOW: 1
-      - name: Check out jspecify/samples-google-prototype
+      - name: Check out jspecify/samples-google-prototype-eisop
         if: always()
         run: |
-          git fetch --depth=1 origin samples-google-prototype
-          git checkout samples-google-prototype
+          git fetch --depth=1 origin samples-google-prototype-eisop
+          git checkout samples-google-prototype-eisop
         working-directory: jspecify
       - name: Run Samples Tests
         if: always()

tests/minimal/Demo.java

@@ -18,7 +18,7 @@
 @NullMarked
 class Demo {
   Object mismatch(@Nullable Object o) {
-    // jspecify_nullness_mismatch
+    // :: error: jspecify_nullness_mismatch
     return o;
   }
 }