[offload] Fix git config arg.

Args passed with -c need to be k=v.

Bug: 59974
Change-Id: I786e457e8de1f75ed32b0e327746a5b492f227f6
Reviewed-on: https://fuchsia-review.googlesource.com/c/jiri/+/430415
Reviewed-by: Anirudh Mathukumilli <rudymathu@google.com>
Commit-Queue: Nathan Mulcahey <nmulcahey@google.com>
diff --git a/gitutil/git.go b/gitutil/git.go
index 85d218e..8ac80da 100644
--- a/gitutil/git.go
+++ b/gitutil/git.go
@@ -324,7 +324,7 @@
 			}
 		case OffloadPackfilesOpt:
 			if typedOpt {
-				args = append([]string{"-c", "fetch.uriprotocols", "https"}, args...)
+				args = append([]string{"-c", "fetch.uriprotocols=https"}, args...)
 			}
 		}
 	}