Invalid read access of chars of narrow string

Invalid read access of chars of narrow string

[Austin Robinson]

Hi!

On one of my computers (Intel® Core™ i9-14900KF), I get the following error when I try to `guix pull`:

```
$ guix pull
Updating channel 'guix' from Git repository at 'https://git.savannah.gnu.org/git/guix.git'...
Authenticating channel 'guix', commits 9edb3f6 to 99a81b6 (34,582 new commits)...
[##                                                                                                                                                                                                 ]Backtrace:
In guix/store.scm:
   1323:3 19 (_)
   1300:8 18 (call-with-build-handler #<procedure 7ff0c7462000 at g…> …)
In guix/scripts/pull.scm:
   864:26 17 (_)
In guix/channels.scm:
    532:7 16 (loop _ _)
In guix/combinators.scm:
    48:26 15 (fold2 #<procedure 7ff0c7453a20 at guix/channels.scm:5…> …)
In guix/channels.scm:
   542:29 14 (_ #<<channel> name: guix url: "https://git.savannah.g…> …)
   421:12 13 (latest-channel-instance #<store-connection 256.99 7ff…> …)
In guix/git.scm:
    300:7 12 (call-with-repository _ _)
In guix/git-authenticate.scm:
   442:22 11 (authenticate-repository _ _ _ #:keyring-reference _ # _ …)
In guix/progress.scm:
    71:36 10 (call-with-progress-reporter _ _)
In srfi/srfi-1.scm:
   460:18  9 (fold #<procedure 7ff0cd4180c0 at guix/git-authenticat…> …)
In guix/git-authenticate.scm:
   290:24  8 (_ #<git-commit f3e17f9ff1bf77b4ebddf0de3340e77e2ec8a8…> …)
    226:4  7 (authenticate-commit #<git-repository 2266af0> #<git-c…> …)
   116:22  6 (commit-signing-key _ #<oid f3e17f9ff1bf77b4ebddf0de33…> …)
In guix/openpgp.scm:
  1088:31  5 (string->openpgp-packet _)
  1074:36  4 (read-radix-64 _)
In gcrypt/base64.scm:
   174:21  3 (base64-decode "iQKTBAABCgB9FiEEPonu50WOcg2XVOCyXiijOw…" …)
In unknown file:
           2 (string-index "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklm…" …)
In ice-9/boot-9.scm:
  1685:16  1 (raise-exception _ #:continuable? _)
  1685:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
Invalid read access of chars of narrow string: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
```

This happens both when I run it from the Guix installation media, or when I'm using Guix on top of another GNU/Linux distribution. I can provide more info if needed or useful.