gRPC errors on push from using bst 1.93.3 caching

Summary

The following gRPC errors are observed when using bst 1.93.3 and buildbox 0.07

[00:00:34][07b3a35c][    push:bootstrap/pcre-build-deps.bst ] FAILURE Failed to push artifact blobs: Unexpected error in RPC handling
        Printing the last 80 lines from log file:
        /builds/freedesktop-sdk/freedesktop-sdk/cache/buildstream/logs/freedesktop-sdk/bootstrap-pcre-build-deps/07b3a35c-push.1102.log
        ======================================================================
        [--:--:--] START   bootstrap/pcre-build-deps.bst: Push
        [--:--:--] LOG     bootstrap/pcre-build-deps.bst: Build environment for element bootstrap/pcre-build-deps.bst
            PATH: /usr/bin:/bin:/usr/sbin:/sbin
            SHELL: /bin/sh
            TERM: dumb
            USER: tomjon
            USERNAME: tomjon
            LOGNAME: tomjon
            LC_ALL: en_US.UTF-8
            HOME: /tmp
            TZ: UTC
            SOURCE_DATE_EPOCH: '1320937200'
            CFLAGS: '-O2 -g -pipe -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions
              -fstack-protector-strong -grecord-gcc-switches -fasynchronous-unwind-tables -fstack-clash-protection '
            CXXFLAGS: '-O2 -g -pipe -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions
              -fstack-protector-strong -grecord-gcc-switches -fasynchronous-unwind-tables -fstack-clash-protection '
            LDFLAGS: '-Wl,-z,relro,-z,now -Wl,--as-needed '
            PYTHON: /usr/bin/python3
            PYTHONHASHSEED: '0'
        [--:--:--] STATUS  bootstrap/pcre-build-deps.bst: Pushing data from artifact 07b3a35c -> https://push.public.aws.celduin.co.uk
        [00:00:34] FAILURE bootstrap/pcre-build-deps.bst: Failed to push artifact blobs: Unexpected error in RPC handling
        ======================================================================

Steps to reproduce

A representive CI job can be seen at https://gitlab.com/freedesktop-sdk/freedesktop-sdk/-/jobs/542055129

Other relevant information

This is not seen with 1.93.1, see libreml/libreml!270 (merged)

There is extensive discussion at celduin/infrastructure/celduin-infra#144 (closed)

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