typing: fix a syntax error in mercurial/cext/bdiff.pyi
I noticed because `merge-pyi` on the non-cext implementations with this file as
input skipped the return type for this. `pytype-single --parse-pyi` confirmed
it was a problem.
=== property cache ===
calllog: []
cached value (unfiltered): NOCACHE
= first access on unfiltered, should do a call
access: 0
calllog: [0]
cached value (unfiltered): 0
= second access on unfiltered, should not do call
access 0
calllog: [0]
cached value (unfiltered): 0
= first access on "visible" view, should do a call
cached value ("visible" view): NOCACHE
access: 7
calllog: [0, 7]
cached value (unfiltered): 0
cached value ("visible" view): 7
= second access on "visible view", should not do call
access: 7
calllog: [0, 7]
cached value (unfiltered): 0
cached value ("visible" view): 7
= no effect on other view
cached value ("immutable" view): NOCACHE
access: 9
calllog: [0, 7, 9]
cached value (unfiltered): 0
cached value ("visible" view): 7
cached value ("immutable" view): 9
=== unfiltered property cache ===
unficalllog: []
cached value (unfiltered): NOCACHE
cached value ("visible" view): NOCACHE
cached value ("immutable" view): NOCACHE
= first access on unfiltered, should do a call
access (unfiltered): 100
unficalllog: [100]
cached value (unfiltered): 100
= second access on unfiltered, should not do call
access (unfiltered): 100
unficalllog: [100]
cached value (unfiltered): 100
= access on view should use the unfiltered cache
access (unfiltered): 100
access ("visible" view): 100
access ("immutable" view): 100
unficalllog: [100]
cached value (unfiltered): 100
cached value ("visible" view): NOCACHE
cached value ("immutable" view): NOCACHE
= even if we clear the unfiltered cache
cached value (unfiltered): NOCACHE
cached value ("visible" view): NOCACHE
cached value ("immutable" view): NOCACHE
unficalllog: [100]
access ("visible" view): 100
unficalllog: [100, 100]
cached value (unfiltered): 100
cached value ("visible" view): NOCACHE
cached value ("immutable" view): NOCACHE
access ("immutable" view): 100
unficalllog: [100, 100]
cached value (unfiltered): 100
cached value ("visible" view): NOCACHE
cached value ("immutable" view): NOCACHE
access (unfiltered): 100
unficalllog: [100, 100]
cached value (unfiltered): 100
cached value ("visible" view): NOCACHE
cached value ("immutable" view): NOCACHE