Test/Eevee: Increase failure threshold for image tests.

Makes the current test cases pass on NVIDIA 1080Ti/515.
The tests still fail on other platforms (AMD, Intel). Some are actual failures.
Other require platform specific reference images.

Original patch provided by Brecht van Lommel.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D15264

tests/python/eevee_render_tests.py

@@ -7,6 +7,7 @@ import shlex
 import shutil
 import subprocess
 import sys
+from pathlib import Path
 
 
 def setup():
@@ -138,6 +139,11 @@ def main():
     report.set_pixelated(True)
     report.set_reference_dir("eevee_renders")
     report.set_compare_engine('cycles', 'CPU')
+
+    test_dir_name = Path(test_dir).name
+    if test_dir_name.startswith('image'):
+        report.set_fail_threshold(0.051)
+
     ok = report.run(test_dir, blender, get_arguments, batch=True)
 
     sys.exit(not ok)