tests: add missing cstdint include for gcc13 (#26792)

See also 853691dfe7

Signed-off-by: Karl Palsson <karlp@tweak.au>
diff --git a/src/app/tests/suites/pics/PICSBooleanExpressionParser.h b/src/app/tests/suites/pics/PICSBooleanExpressionParser.h
index a9ecd8b..162f55d 100644
--- a/src/app/tests/suites/pics/PICSBooleanExpressionParser.h
+++ b/src/app/tests/suites/pics/PICSBooleanExpressionParser.h
@@ -21,6 +21,7 @@
  *        implements PICS condition parsing for YAML tests.
  */
 
+#include <cstdint>
 #include <map>
 #include <string>
 #include <vector>