Roll recipe dependencies (trivial).

This is an automated CL created by the recipe roller. This CL rolls
recipe changes from upstream projects (fuchsia, recipe_engine) into this repository.

The build that created this CL was
https://ci.chromium.org/b/8779605689365197281

fuchsia:
https://fuchsia.googlesource.com/infra/recipes/+log/6cffb72af791703ff7610681937b52d7633dee13~..6b1d3e7ffa6d18a29ff858ca8551a18a61f904fe
  6cffb72 (nmulcahey@google.com)
      [rust_toolchain] Add `aarch64-apple-darwin`
  780460b (global-integration-roller@fuchsia-infra.iam.gserviceaccount.com)
      [roll] Update pinned tools
  6b1d3e7 (global-integration-roller@fuchsia-infra.iam.gserviceaccount.com)
      [roll] Update pinned tools

recipe_engine:
https://chromium.googlesource.com/infra/luci/recipes-py/+/8fc4e6c80e522c4bdcc2b04676c3eb5bde9a1580
  8fc4e6c (iannucci@chromium.org)
      [recipes.py] Unset PYTHONPATH in case users have conflicting va...

Please check the following references for more information:
- autoroller, https://chromium.googlesource.com/infra/luci/recipes-py/+/main/doc/workflow.md#autoroller
- rollback, https://chromium.googlesource.com/infra/luci/recipes-py/+/main/doc/workflow.md#rollback
- cross-repo dependencies, https://chromium.googlesource.com/infra/luci/recipes-py/+/main/doc/cross_repo.md

Use https://goo.gl/noib3a to file a bug.

Recipe-Tryjob-Bypass-Reason: Autoroller
Ignore-Freeze: Autoroller
Bugdroid-Send-Email: False
Change-Id: I6e537367efb06a5ec31e94fc22f9260d9c120a14
Reviewed-on: https://pigweed-review.googlesource.com/c/infra/recipes/+/149650
Bot-Commit: Recipe Deps Roller <recipe-deps-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Recipe Deps Roller <recipe-deps-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/infra/config/recipes.cfg b/infra/config/recipes.cfg
index 094eccf..5f5e95b 100644
--- a/infra/config/recipes.cfg
+++ b/infra/config/recipes.cfg
@@ -17,12 +17,12 @@
   "deps": {
     "fuchsia": {
       "branch": "refs/heads/main",
-      "revision": "4920d6892fbb4fd087debcb9ff01ff63c350edab",
+      "revision": "6b1d3e7ffa6d18a29ff858ca8551a18a61f904fe",
       "url": "https://fuchsia.googlesource.com/infra/recipes"
     },
     "recipe_engine": {
       "branch": "refs/heads/main",
-      "revision": "b60bb0d221df01a41a175daf18632ec0525f20f1",
+      "revision": "8fc4e6c80e522c4bdcc2b04676c3eb5bde9a1580",
       "url": "https://chromium.googlesource.com/infra/luci/recipes-py"
     }
   },
diff --git a/recipes.py b/recipes.py
index cccaaf3..5f23b3f 100755
--- a/recipes.py
+++ b/recipes.py
@@ -235,6 +235,14 @@
   if not shutil.which(vpython):
     return f'Required binary is not found on PATH: {vpython}'
 
+  # We unset PYTHONPATH here in case the user has conflicting environmental
+  # things we don't want them to leak through into the recipe_engine which
+  # manages its environment entirely via vpython.
+  #
+  # NOTE: os.unsetenv unhelpfully doesn't exist on all platforms until python3.9
+  # so we have to use the cutesy `pop` formulation below until then...
+  os.environ.pop("PYTHONPATH", None)
+
   argv = ([
     vpython, '-u', os.path.join(engine_path, 'recipe_engine', 'main.py'),
   ] + args)