[3.11] Fix Windows build regen with Python 3.15 as the host Python (#160621)

The windows-2022 GitHub runner image no longer ships Python 3.10, so
PCbuild/find_python.bat fell through to NuGet and installed the latest
pythonx86 package, which is now 3.15.1. Python 3.15 removed
Loader.load_module(), which Python/makeopcodetargets.py used to import
Lib/opcode.py, so the _RegenOpcodes target failed and broke every
Windows CI build on this branch.

Load Lib/opcode.py through importlib.util instead, and extend the py.exe
search list in find_python.bat up to 3.14 so the build picks up the
runner's preinstalled Python rather than whatever NuGet considers latest.

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

Author: ambv

PCbuild/find_python.bat

@@ -42,7 +42,7 @@
 @if NOT "%HOST_PYTHON%"=="" @%HOST_PYTHON% -Ec "import sys; assert sys.version_info[:2] >= (3, 9)" >nul 2>nul && (set PYTHON="%HOST_PYTHON%") && (set _Py_Python_Source=found as HOST_PYTHON) && goto :found
 
 @rem If py.exe finds a recent enough version, use that one
-@for %%p in (3.10 3.9) do @py -%%p -EV >nul 2>&1 && (set PYTHON=py -%%p) && (set _Py_Python_Source=found %%p with py.exe) && goto :found
+@for %%p in (3.14 3.13 3.12 3.11 3.10 3.9) do @py -%%p -EV >nul 2>&1 && (set PYTHON=py -%%p) && (set _Py_Python_Source=found %%p with py.exe) && goto :found
 
 @if NOT exist "%_Py_EXTERNALS_DIR%" mkdir "%_Py_EXTERNALS_DIR%"
 @set _Py_NUGET=%NUGET%

Python/makeopcodetargets.py

@@ -3,28 +3,20 @@
 (for compilers supporting computed gotos or "labels-as-values", such as gcc).
 """
 
+import importlib.util
 import os
 import sys
 
 
-try:
-    from importlib.machinery import SourceFileLoader
-except ImportError:
-    import imp
-
-    def find_module(modname):
-        """Finds and returns a module in the local dist/checkout.
-        """
-        modpath = os.path.join(
-            os.path.dirname(os.path.dirname(__file__)), "Lib")
-        return imp.load_module(modname, *imp.find_module(modname, [modpath]))
-else:
-    def find_module(modname):
-        """Finds and returns a module in the local dist/checkout.
-        """
-        modpath = os.path.join(
-            os.path.dirname(os.path.dirname(__file__)), "Lib", modname + ".py")
-        return SourceFileLoader(modname, modpath).load_module()
+def find_module(modname):
+    """Finds and returns a module in the local dist/checkout.
+    """
+    modpath = os.path.join(
+        os.path.dirname(os.path.dirname(__file__)), "Lib", modname + ".py")
+    spec = importlib.util.spec_from_file_location(modname, modpath)
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
 
 
 def write_contents(f):