Tests: enable VSE blend modes tests

The actual files for them and reference results were added several
years ago, but the tests themselves were never enabled

Pull Request: https://projects.blender.org/blender/blender/pulls/127898

tests/python/CMakeLists.txt

@@ -1111,6 +1111,8 @@ else()
     effects
     filter
     transform
+    blend_modes_byte
+    blend_modes_float
   )
 
   foreach(render_test ${render_tests})

tests/python/sequencer_render_tests.py

@@ -50,11 +50,7 @@ def main():
     report = render_report.Report("Sequencer", output_dir, oiiotool)
     report.set_pixelated(True)
     # Default error tolerances are quite large, lower them.
-    report.set_fail_threshold(1.0 / 255.0)
-    if os.path.basename(test_dir) == "effects":
-        # Effects test uses input images with nan/inf values on purpose,
-        # and they have slightly more variance between platforms.
-        report.set_fail_threshold(2.0 / 255.0)
+    report.set_fail_threshold(2.0 / 255.0)
     report.set_fail_percent(0.01)
     report.set_reference_dir("reference")