roll: pigweed, pw_toolchain: bazel: Use Python toolchain in custom rules

This will make the bzlmod transition smoother (by removing the @python3
reference: in the bzlmod version of rules_python this repo doesn't exist
any more). The Python toolchain is the right way to access the
interpreter anyway.

This is a reland of http://pwrev.dev/224272. The original change had an
unlucky mid-air collision with http://pwrev.dev/204199. However, I also
took the opportunity to fix the toolchain type to the
exec_tools_toolchain_type (see https://pwbug.dev/258836641#comment59 for
more).

Original-Bug: 258836641
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/224298
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>

https://pigweed.googlesource.com/pigweed/pigweed
pigweed, pw_toolchain Rolled-Commits: e3076ba724ed431..e45ec8f7c2d1e77
Roller-URL: https://ci.chromium.org/b/8742009187639478177
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Iba87e3a8be1774d6ce88a2a26a727c649ef6b750
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/quickstart/bazel/+/224611
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/WORKSPACE b/WORKSPACE
index 6f89a71..744436c 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -84,8 +84,8 @@
     name = "pigweed",
     # ROLL: Warning: this entry is automatically updated.
     # ROLL: Last updated 2024-07-19.
-    # ROLL: By https://cr-buildbucket.appspot.com/build/8742020229069949249.
-    commit = "e3076ba724ed4314daee7d982be6961e19b3392f",
+    # ROLL: By https://cr-buildbucket.appspot.com/build/8742009187639478177.
+    commit = "e45ec8f7c2d1e77258bd1cc9becdc5191bead5bf",
     remote = "https://pigweed.googlesource.com/pigweed/pigweed.git",
 )
 
@@ -93,8 +93,8 @@
     name = "pw_toolchain",
     # ROLL: Warning: this entry is automatically updated.
     # ROLL: Last updated 2024-07-19.
-    # ROLL: By https://cr-buildbucket.appspot.com/build/8742020229069949249.
-    commit = "e3076ba724ed4314daee7d982be6961e19b3392f",
+    # ROLL: By https://cr-buildbucket.appspot.com/build/8742009187639478177.
+    commit = "e45ec8f7c2d1e77258bd1cc9becdc5191bead5bf",
     remote = "https://pigweed.googlesource.com/pigweed/pigweed.git",
     strip_prefix = "pw_toolchain_bazel",
 )