tests/: fix test failures with sysinstalls.

We allow small differences in generated page bitmaps, which can occur due to
different third-party libraries in sysinstalls.

Author: julian-smith-artifex-com

tests/test_annots.py

@@ -416,4 +416,6 @@ def test_3863():
             print(f'{path_png=}.')
             print(f'{path_png_expected=}.')
             rms = gentle_compare.pixmaps_rms(path_png, path_png_expected, '    ')
-            assert rms == 0
+            # We get small differences in sysinstall tests, where some
+            # thirdparty libraries can differ.
+            assert rms < 1

tests/test_general.py

@@ -1380,4 +1380,6 @@ def test_3624():
         if pymupdf.mupdf_version_tuple < (1, 24, 10):
             assert rms > 12
         else:
-            assert rms == 0
+            # We get small differences in sysinstall tests, where some
+            # thirdparty libraries can differ.
+            assert rms < 1