We are populating, but never releasing two string buffers in
`format_trailers()`, causing a memory leak. Plug this leak by lifting
those buffers outside of the loop and releasing them on function return.
This fixes the memory leaks, but also optimizes the loop as we don't
have to reallocate the buffers on every single iteration.

Signed-off-by: Patrick Steinhardt <redacted>
---
 t/t7513-interpret-trailers.sh |  1 +
 trailer.c                     | 13 ++++++++-----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/t/t7513-interpret-trailers.sh b/t/t7513-interpret-trailers.sh
index 0f7d8938d98..38d6ccaa001 100755
--- a/t/t7513-interpret-trailers.sh
+++ b/t/t7513-interpret-trailers.sh

@@ -5,6 +5,7 @@

 test_description='git interpret-trailers'

+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh

 # When we want one trailing space at the end of each line, let's use sed

diff --git a/trailer.c b/trailer.c
index f1eca6d5d15..24e4e56fdf8 100644
--- a/trailer.c
+++ b/trailer.c

@@ -1111,16 +1111,19 @@ void format_trailers(const struct process_trailer_options *opts,
 		     struct list_head *trailers,
 		     struct strbuf *out)
 {
+	struct strbuf tok = STRBUF_INIT;
+	struct strbuf val = STRBUF_INIT;
 	size_t origlen = out->len;
 	struct list_head *pos;
 	struct trailer_item *item;

+
 	list_for_each(pos, trailers) {
 		item = list_entry(pos, struct trailer_item, list);
 		if (item->token) {
-			struct strbuf tok = STRBUF_INIT;
-			struct strbuf val = STRBUF_INIT;
+			strbuf_reset(&tok);
 			strbuf_addstr(&tok, item->token);
+			strbuf_reset(&val);
 			strbuf_addstr(&val, item->value);