add pylint to list of required linting tools

With pylint being run in the CI, passing it is required now.

CMakeLists.txt

@@ -155,6 +155,10 @@ if (BUILD_TESTS)
     add_test(NAME phpcs
              COMMAND phpcs --report-width=120 --colors lib website utils
              WORKING_DIRECTORY ${PROJECT_SOURCE_DIR})
+
+    add_test(NAME pylint
+             COMMAND pylint3 nominatim
+             WORKING_DIRECTORY ${PROJECT_SOURCE_DIR})
 endif()
 
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