Fix sphinx-doc#9096: sphinx-build: the value of progress bar for para…

…lle build is wrong

The value of progress bar (reading and writing) should be increased just after
each task is finished.

CHANGES

@@ -39,6 +39,7 @@ Bugs fixed
 
 * #9575: autodoc: The annotation of return value should not be shown when
   ``autodoc_typehints="description"``
+* #9096: sphinx-build: the value of progress bar for paralle build is wrong
 
 Testing
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