commit-msg: Match the Signed-off-by line with name and mail address

The previous regular expression only matches the line starting with
"Signed-off-by:". If the name and mail address are missing, it can not
find out. The following words should be "name <mail@xxx.com>".

Change-Id: I42cc399e79b65928a6aef87c51e5476c7158d166
Signed-off-by: Zheng Bao <fishbaozi@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/73340
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>

util/gitconfig/commit-msg

@@ -166,7 +166,7 @@ _gen_ChangeId() {
 	git hash-object -t commit --stdin
 }
 
-if ! grep -qi '^[[:space:]]*Signed-off-by:' "$MSG"; then
+if ! grep -qi '^[[:space:]]*Signed-off-by:.\+<.\+@.\+>' "$MSG"; then
 	printf "\nError: No Signed-off-by line in the commit message.\n"
 	exit 1
 fi