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gh-115398: Revert `PyExpat_CAPI_MAGIC` version bump (GH-116411) 

Revert "gh-115398: Increment PyExpat_CAPI_MAGIC for SetReparseDeferralEnabled addition (GH-116301)"

This reverts part of commit eda2963378.  Why? this comment buried in an earlier code review explains:

I checked again how that value is used in practice, it's here:

0c80da4c14/Modules/_elementtree.c (L4363-L4372)

Based on that code my understanding is that loading bigger structs from the future is considered okay unless `PyExpat_CAPI_MAGIC` differs, which implies that (1) magic needs to stay the same to support loading the future from the past and (2) that `PyExpat_CAPI_MAGIC` should only ever change for changes that do not increase size (but keep it constant).

To summarize, that supports your argument.
I checked branches 3.8, 3.9, 3.10, 3.11, 3.12 now and they all have the same comparison code there so reverting that magic string bump will support seamless backporting.
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Sebastian Pipping 2024-03-06 18:55:07 +01:00 committed by GitHub
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commit 8a8e9204d1
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Include/pyexpat.h
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@ -3,7 +3,7 @@
/* note: you must import expat.h before importing this module! */
#define PyExpat_CAPI_MAGIC "pyexpat.expat_CAPI 1.2"
#define PyExpat_CAPI_MAGIC "pyexpat.expat_CAPI 1.1"
#define PyExpat_CAPSULE_NAME "pyexpat.expat_CAPI"
struct PyExpat_CAPI