Fix various trivial problems (#36953)

1. remove `TEST_CONFLICTING_PATCHES_WITH_GIT_APPLY`
* it defaults to false and is unlikely to be useful for most users (see
#22130)
* with new git versions (>= 2.40), "merge-tree" is used,
"checkConflictsByTmpRepo" isn't called, the option does nothing.
2. fix fragile `db.Cell2Int64` (new: `CellToInt`)
3. allow more routes in maintenance mode (e.g.: captcha)
4. fix MockLocale html escaping to make it have the same behavior as
production locale

modules/setting/repository.go

@@ -86,7 +86,6 @@ var (
 			DefaultMergeMessageOfficialApproversOnly bool
 			PopulateSquashCommentWithCommitMessages  bool
 			AddCoCommitterTrailers                   bool
-			TestConflictingPatchesWithGitApply       bool
 			RetargetChildrenOnMerge                  bool
 			DelayCheckForInactiveDays                int
 			DefaultDeleteBranchAfterMerge            bool
@@ -211,7 +210,6 @@ var (
 			DefaultMergeMessageOfficialApproversOnly bool
 			PopulateSquashCommentWithCommitMessages  bool
 			AddCoCommitterTrailers                   bool
-			TestConflictingPatchesWithGitApply       bool
 			RetargetChildrenOnMerge                  bool
 			DelayCheckForInactiveDays                int
 			DefaultDeleteBranchAfterMerge            bool