Fix spellings (#12277) [backport]

lib/impure/db_odbc.nim

@@ -303,7 +303,7 @@ iterator instantRows*(db: var DbConn, query: SqlQuery,
                       args: varargs[string, `$`]): InstantRow
                 {.tags: [ReadDbEffect, WriteDbEffect].} =
   ## Same as fastRows but returns a handle that can be used to get column text
-  ## on demand using []. Returned handle is valid only within the interator body.
+  ## on demand using []. Returned handle is valid only within the iterator body.
   var
     rowRes: Row = @[]
     sz: TSqlInteger = 0

lib/impure/db_postgres.nim

@@ -182,7 +182,7 @@ proc setRow(res: PPGresult, r: var Row, line, cols: int32) =
 iterator fastRows*(db: DbConn, query: SqlQuery,
                    args: varargs[string, `$`]): Row {.tags: [ReadDbEffect].} =
   ## executes the query and iterates over the result dataset. This is very
-  ## fast, but potenially dangerous: If the for-loop-body executes another
+  ## fast, but potentially dangerous: If the for-loop-body executes another
   ## query, the results can be undefined. For Postgres it is safe though.
   var res = setupQuery(db, query, args)
   var L = pqnfields(res)

lib/impure/nre.nim

@@ -137,7 +137,7 @@ type
     ## into PCRE flags. These include ``NEVER_UTF``, ``ANCHORED``,
     ## ``DOLLAR_ENDONLY``, ``FIRSTLINE``, ``NO_AUTO_CAPTURE``,
     ## ``JAVASCRIPT_COMPAT``, ``U``, ``NO_STUDY``. In other PCRE wrappers, you
-    ## will need to pass these as seperate flags to PCRE.
+    ## will need to pass these as separate flags to PCRE.
     pattern*: string  ## not nil
     pcreObj: ptr pcre.Pcre  ## not nil
     pcreExtra: ptr pcre.ExtraData  ## nil