Fix upload tests in new year

I’m not sure why I included the year number in the file name in
f6e28b5 (probably to limit the number of file versions?), but this
made the tests fail in 2024: we expect warnings for the same content in
older versions of the same file, but not in other files. Add that.

    {"result":"Warning","warnings":{"duplicate":["M3api_test_file_2023.svg"]},"filekey":"...","sessionkey":"..."}

test/integration/node.test.js

@@ -195,8 +195,16 @@ describe( 'NodeSession', function () {
 					continue;
 				}
 
-				delete warnings.exists;
-				delete warnings.duplicateversions;
+				// handle warnings about the same content already existing
+				delete warnings.exists; // file already exists
+				delete warnings.duplicateversions; // same content in old version of same file
+				if ( 'duplicate' in warnings ) {
+					// same content in file from earlier years?
+					if ( warnings.duplicate.every( ( name ) => name.startsWith( 'M3api_test_file_' ) ) ) {
+						delete warnings.duplicate;
+					}
+				}
+
 				if ( Object.keys( warnings ).length === 0 ) {
 					// ignore these specific warnings, repeat by file key
 					expect( upload ).to.have.property( 'filekey' );