fix(core): do not assume rules_python runtime (#3134)

This change reverts the behaviour where we assume that particular
attributes will be always present - if bazel is doing autoloading for
WORKSPACE builds (7.6.1), then we will crash with attribute error.

I could not think how to add a unit test, which would test this fix
because it seems to only happen with a released version of rules_python
where we are not using `local_repository` override.

Fixes #3119

---------

Co-authored-by: Richard Levasseur <richardlev@gmail.com>

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 04979e8..b235989 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -109,6 +109,8 @@
 * (toolchains) use "command -v" to find interpreter in `$PATH`
   ([#3150](https://github.com/bazel-contrib/rules_python/pull/3150)).
 * (pypi) `bazel vendor` now works in `bzlmod` ({gh-issue}`3079`).
+* (core) builds work again on `7.x` `WORKSPACE` configurations
+  ([#3119](https://github.com/bazel-contrib/rules_python/issues/3119)).
 
 {#v0-0-0-added}
 ### Added

python/private/py_executable.bzl

diff --git a/python/private/py_executable.bzl b/python/private/py_executable.bzl
index 7e50247..9927975 100644
--- a/python/private/py_executable.bzl
+++ b/python/private/py_executable.bzl
@@ -796,6 +796,7 @@
         is_for_zip,
         runtime_details,
         venv = None):
+    """Create a legacy bootstrap script that is written in Python."""
     runtime = runtime_details.effective_runtime
 
     if venv:
@@ -805,8 +806,11 @@
 
     python_binary_actual = venv.interpreter_actual_path if venv else ""
 
-    # Runtime may be None on Windows due to the --python_path flag.
-    if runtime and runtime.supports_build_time_venv:
+    # Guard against the following:
+    # * Runtime may be None on Windows due to the --python_path flag.
+    # * Runtime may not have 'supports_build_time_venv' if a really old version is autoloaded
+    #   on bazel 7.6.x.
+    if runtime and getattr(runtime, "supports_build_time_venv", False):
         resolve_python_binary_at_runtime = "0"
     else:
         resolve_python_binary_at_runtime = "1"