fix: ensure consistent coverage compilation flags across all CI test steps

The test-coverage CI workflow was building the library with coverage flags
but then running certain tests without those flags, causing compilation
interface mismatches. This resulted in implicit interface errors for the
contains_unicode function despite it being properly declared in the module.

Fixed by adding coverage flags to both test_system_fpm_example and
test_system_cmake_example test steps to maintain compilation consistency.

Resolves CI failures on PR #369 for test-coverage and ensures all test
steps use the same compilation flags as the library build.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: krystophny

.github/workflows/test-coverage.yml

@@ -88,11 +88,11 @@ jobs:
 
     - name: Test FPM example build
       run: |
-        make test ARGS="--target test_system_fpm_example"
+        make test ARGS="--target test_system_fpm_example --flag '-fprofile-arcs -ftest-coverage'"
 
     - name: Test CMake example build
       run: |
-        make test ARGS="--target test_system_cmake_example"
+        make test ARGS="--target test_system_cmake_example --flag '-fprofile-arcs -ftest-coverage'"
 
     - name: Validate PNG output with PIL
       continue-on-error: true