gh-119180: Update the magic number

[JelleZijlstra]

PR #119321 added a comment about the magic number bump
but did not actually apply the new magic number.

Also, update PC/launcher.c.

• Issue: Implement PEP 649 and PEP 749 #119180

[Eclips4]

I've probably found a typo:

cpython/Lib/importlib/_bootstrap_external.py

Line 475 in d472b4f

# Python 3.14a1 3600 (Add LOAD_COMMON_CONSTANT)

Since we are at a0 now, there's should be 3.14a0, isn't it?
If so, I think we can address that in this PR :)

[JelleZijlstra]

a1 is right; the change is expected to be released in a1. You can see a little further up that there were numerous changes listed as 3.13a1 but none for 3.13a0.

[Eclips4]

a1 is right; the change is expected to be released in a1. You can see a little further up that there were numerous changes listed as 3.13a1 but none for 3.13a0.

I was confused by an older entries where's a0 is used:

cpython/Lib/importlib/_bootstrap_external.py

Lines 354 to 356 in c9073eb

	# Python 3.9a0 3420 (add LOAD_ASSERTION_ERROR #34880)
	# Python 3.9a0 3421 (simplified bytecode for with blocks #32949)
	# Python 3.9a0 3422 (remove BEGIN_FINALLY, END_FINALLY, CALL_FINALLY, POP_FINALLY bytecodes #33387)

It seems that the policy has changed since then?