context: convert to hex for error message only for 20-byte changeid
Now that 20-byte strings unambiguously mean binary (or a bug), we can
specialize the conversion to hex for that case.
Differential Revision: https://phab.mercurial-scm.org/D3452
missed keys: oid, size
ok
unexpected value: version='https://unknown.github.com/spec/v1'
cannot parse git-lfs text: 'version https://git-lfs.github.com/spec/v1\n\noid sha256:4d7a214614ab2935c943f9e0ff69d22eadbb8f32b1258daaa5e2ca24d17e2393\nsize 12345\nx-foo extra-information\n'
unexpected value: oid='ahs256:4d7a214614ab2935c943f9e0ff69d22eadbb8f32b1258daaa5e2ca24d17e2393'
unexpected value: oid='4d7a214614ab2935c943f9e0ff69d22eadbb8f32b1258daaa5e2ca24d17e2393'
unexpected value: size='0x12345'
ok
cannot parse git-lfs text: 'version https://git-lfs.github.com/spec/v1\noid sha256:4d7a214614ab2935c943f9e0ff69d22eadbb8f32b1258daaa5e2ca24d17e2393\nsize 12345\nx-foo extra\ninformation\n'
unexpected key: x_foo
missed keys: oid
missed keys: oid, size