deps: bump protobuf-specs

[woodruffw]

Very WIP. This includes underlying changes to the proto models themselves, so I need to go through various internal usages and correct them.

On the plus side, this makes our typechecking of each proto model's internals much more correct.

[woodruffw]

Switching to betterproto's Pydantic models produces generally better-typed results, but it looks like enums are strictly worse:

sigstore/_internal/trust.py:96: error: Argument 1 to <set> has incompatible type "int"; expected "PublicKeyDetails"  [arg-type]
sigstore/_internal/trust.py:97: error: Argument 2 to <set> has incompatible type "int"; expected "PublicKeyDetails"  [arg-type]
sigstore/_internal/trust.py:98: error: Argument 3 to <set> has incompatible type "int"; expected "PublicKeyDetails"  [arg-type]
sigstore/_internal/trust.py:99: error: Argument 4 to <set> has incompatible type "int"; expected "PublicKeyDetails"  [arg-type]
sigstore/_internal/trust.py:103: error: Dict entry 0 has incompatible type "int": "SHA256"; expected "PublicKeyDetails": "HashAlgorithm"  [dict-item]
sigstore/_internal/trust.py:104: error: Dict entry 1 has incompatible type "int": "SHA384"; expected "PublicKeyDetails": "HashAlgorithm"  [dict-item]
sigstore/_internal/trust.py:105: error: Dict entry 2 has incompatible type "int": "SHA512"; expected "PublicKeyDetails": "HashAlgorithm"  [dict-item]
sigstore/models.py:670: error: Incompatible types in assignment (expression has type "dict[str, MessageSignature]", variable has type "MessageSignature | Envelope")  [assignment]
sigstore/models.py:672: error: Incompatible types in assignment (expression has type "dict[str, sigstore_protobuf_specs.io.intoto.Envelope]", variable has type "MessageSignature | sigstore.dsse.Envelope")  [assignment]
sigstore/models.py:674: error: Argument after ** must be a mapping, not "MessageSignature | Envelope"  [arg-type]
Found 10 errors in 2 files (checked [28](https://github.com/sigstore/sigstore-python/actions/runs/12772251322/job/35601345407?pr=1276#step:5:29) source files)
make: *** [Makefile:66: lint] Error 1

I'll look into whether this can be fixed upstream.