CodingGuidelines: allow declaring variables in for loops

Since 44ba10d671 (revision: use C99 declaration of variable in for()
loop, 2021-11-14) released with v2.35.0 we've had a variable declared
with in a for loop.

Since then we've had inadvertent follow-ups to that with at least
cb2607759e (merge-ort: store more specific conflict information,
2022-06-18) released with v2.38.0.

As November 2022 is within the window of this upcoming release,
let's update the guideline to allow this.  We can have the promised
"revisit" discussion while this patch cooks, and drop it if it turns
out that it is still premature, which is not expected to happen at
this moment.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/CodingGuidelines

@@ -232,18 +232,12 @@ For C programs:
    . since early 2021 with 765dc168882, we have been using variadic
      macros, mostly for printf-like trace and debug macros.
 
-   These used to be forbidden, but we have not heard any breakage
-   report, and they are assumed to be safe.
+   . since late 2021 with 44ba10d6, we have had variables declared in
+     the for loop "for (int i = 0; i < 10; i++)".
 
  - Variables have to be declared at the beginning of the block, before
    the first statement (i.e. -Wdeclaration-after-statement).
 
- - Declaring a variable in the for loop "for (int i = 0; i < 10; i++)"
-   is still not allowed in this codebase.  We are in the process of
-   allowing it by waiting to see that 44ba10d6 (revision: use C99
-   declaration of variable in for() loop, 2021-11-14) does not get
-   complaints.  Let's revisit this around November 2022.
-
  - NULL pointers shall be written as NULL, not as 0.
 
  - When declaring pointers, the star sides with the variable