bin/get-pick-list.sh: tweak the commit sha matching pattern

Currently we match on:
 - any arbitrary length of,
 - any a-z A-Z and 0-9 characters

At the same time, a commit sha consists of lowercase hexadecimal
numbers. Any sha shorter than 8 characters is ambiguous - in some cases
even 11+ are required.

So change the pattern to a-f0-9 and adjust the length to 8-40.

As we're here we could use a single grep, instead of the grep/sed combo.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Juan A. Suarez <jasuarez@igalia.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

bin/get-pick-list.sh

@@ -25,7 +25,7 @@ is_fixes_nomination()
 {
 	fixes=`git show --pretty=medium -s $1 | tr -d "\n" | \
 		sed -e 's/fixes:[[:space:]]*/\nfixes:/Ig' | \
-		grep "fixes:" | sed -e 's/\(fixes:[a-zA-Z0-9]*\).*$/\1/'`
+		grep -Eo 'fixes:[a-f0-9]{8,40}'`
 
 	fixes_count=`echo "$fixes" | wc -l`
 	if [ $fixes_count -eq 0 ] ; then