ui-shared: replace 'unsigned char sha1[20]' with 'struct object_id oid'

Upstream git is replacing 'unsigned char sha1[20]' with 'struct object_id
oid'. We have some code that can be changed independent from upstream. So
here we go...

ui-shared.c

@@ -1074,18 +1074,18 @@ void cgit_print_filemode(unsigned short mode)
 void cgit_compose_snapshot_prefix(struct strbuf *filename, const char *base,
 				  const char *ref)
 {
-	unsigned char sha1[20];
+	struct object_id oid;
 
 	/*
 	 * Prettify snapshot names by stripping leading "v" or "V" if the tag
 	 * name starts with {v,V}[0-9] and the prettify mapping is injective,
 	 * i.e. each stripped tag can be inverted without ambiguities.
 	 */
-	if (get_sha1(fmt("refs/tags/%s", ref), sha1) == 0 &&
+	if (get_oid(fmt("refs/tags/%s", ref), &oid) == 0 &&
 	    (ref[0] == 'v' || ref[0] == 'V') && isdigit(ref[1]) &&
-	    ((get_sha1(fmt("refs/tags/%s", ref + 1), sha1) == 0) +
-	     (get_sha1(fmt("refs/tags/v%s", ref + 1), sha1) == 0) +
-	     (get_sha1(fmt("refs/tags/V%s", ref + 1), sha1) == 0) == 1))
+	    ((get_oid(fmt("refs/tags/%s", ref + 1), &oid) == 0) +
+	     (get_oid(fmt("refs/tags/v%s", ref + 1), &oid) == 0) +
+	     (get_oid(fmt("refs/tags/V%s", ref + 1), &oid) == 0) == 1))
 		ref++;
 
 	strbuf_addf(filename, "%s-%s", base, ref);