Merge branch 'bubble-read-errors' into 'master'

Make the keys return their inner error, if any.

See merge request !162
6 jobs for master in 25 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #18201
build:linux

00:00:24

failed #18200
build:linux:stable

00:00:14

passed #18202
build:redox

00:00:25

 
  Test
skipped #18204
test:linux
skipped #18203
test:linux:stable
skipped #18205
test:redox
 
Name Stage Failure
failed
build:linux:stable Build
Removing target/

Skipping Git submodules setup
Checking cache for default...
No URL provided, cache will not be downloaded from shared cache server. Instead a local version of cache will be extracted.
Successfully extracted cache
$ cargo +stable build --verbose
error: toolchain 'stable-x86_64-unknown-linux-gnu' is not installed
ERROR: Job failed: exit code 1