Test unused static variable with side-effecting initializer

Add a minimal initializer that increments a global and record the current unused-static-variable alert as spurious.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jketema

cpp/ql/test/query-tests/Best Practices/Unused Entities/UnusedStaticVariables/UnusedStaticVariables.expected

@@ -2,3 +2,4 @@
 | test.cpp:8:12:8:21 | staticVar6 | Static variable staticVar6 is never read. |
 | test.cpp:10:11:10:19 | constVar8 | Static variable constVar8 is never read. |
 | test.cpp:12:12:12:22 | staticVar10 | Static variable staticVar10 is never read. |
+| test.cpp:38:12:38:22 | initialized | Static variable initialized is never read. |

cpp/ql/test/query-tests/Best Practices/Unused Entities/UnusedStaticVariables/test.cpp

@@ -29,3 +29,10 @@ class MyTemplateClass // never instantiated
 		// ...
 	}
 };
+
+int initialize()
+{
+	return ++globalVar;
+}
+
+static int initialized = initialize(); // $ SPURIOUS: Alert // GOOD (initializer has a side effect)