recipes.cfg: update all branches to main

All repositories have main branch and it's default branch

R=ehmaldonado@chromium.org

Change-Id: I1206574901124012254948095c5a3450b8449517
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2939020
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Auto-Submit: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>

infra/config/recipes.cfg

@@ -15,7 +15,7 @@
   "canonical_repo_url": "https://chromium.googlesource.com/chromium/tools/depot_tools.git",
   "deps": {
     "recipe_engine": {
-      "branch": "master",
+      "branch": "main",
       "revision": "9ab7500f8445230c5ad638838546c8281c4eee45",
       "url": "https://chromium.googlesource.com/infra/luci/recipes-py.git"
     }