Fix typos in documentation and code comments which repeat various words.
These typos were found by searching using scripts like this:
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Signed-off-by: Andrei Rybak <redacted>
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diff --git a/t/t6416-recursive-corner-cases.sh b/t/t6416-recursive-corner-cases.sh

@@ -871,7 +871,7 @@ test_expect_failure 'merge of D2 & E4 merges a2s & reports conflict for a/file'
 # it feels sound to say "B and C do not agree what the final pathname
 # should be, but we know this content was derived from the common A:a so we
 # use one path whose name is arbitrary in the virtual merge base X between
-# D and E" and then further let the rename detection to notice that that
+# D and E" and then further let the rename detection to notice that
 # arbitrary path gets renamed between X-D to "newname" and X-E also to
 # "newname" to resolve it as both sides renaming it to the same new
 # name. It is akin to what we do at the content level, i.e. "B and C do not