roll: third_party/pigweed: pw_env_setup: Add check for git in _check_submodule_presence

If the checkout isn't using git (Cog), don't try updating
git submodules.

Test: confirmed check passes when using git
Test: confirmed check fails when using Cog
Original-Bug: 365557573
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/234212

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: ae663f3530e69e9..16f0f6387505dc2
Roller-URL: https://ci.chromium.org/b/8737248191881030401
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ie10e5b6ab0178a6eb2bdd0b09497f58ef0879126
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/234733
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index ae663f3..16f0f63 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit ae663f3530e69e9c3114950116c170f3e7a35b9b
+Subproject commit 16f0f6387505dc27e7c1a76387b05524752b4602