Installing a major version does not allow overriding a minor version on the command line

Problem

Installing 1.33 does not allow running cargo +1.33.0. You have to explicitly use cargo +1.33.

Steps

1. rustup install 1.33
2. cargo +1.33.0

error: toolchain '1.33.0-x86_64-unknown-linux-gnu' is not installed

Possible Solution(s)

• Make it work as-is, and have 1.33.0 forward to 1.33. Using 1.33.1 should give an error (and possibly suggest using 1.33 instead).
• Give a better error that suggests using 1.33 instead.

Notes

Output of rustup --version:

rustup 1.23.1 (3df2264a9 2020-11-30)
info: This is the version for the rustup toolchain manager, not the rustc compiler.
info: The currently active `rustc` version is `rustc 1.48.0 (7eac88abb 2020-11-16)`

Output of rustup show:

Default host: x86_64-unknown-linux-gnu
rustup home:  /home/joshua/.local/lib/rustup

installed toolchains
--------------------

stable-x86_64-unknown-linux-gnu (default)
beta-x86_64-unknown-linux-gnu
nightly-2020-11-25-x86_64-unknown-linux-gnu
nightly-x86_64-unknown-linux-gnu
1.33-x86_64-unknown-linux-gnu

active toolchain
----------------

stable-x86_64-unknown-linux-gnu (default)
rustc 1.48.0 (7eac88abb 2020-11-16)

Reproduce the behavior with rustup install 1.33 followed by cargo +1.33.0, and compare it with cargo +1.33. Trace the rustup toolchain-resolution entry point used by the command-line override; done means the requested major-minor version behaves as described, or the error clearly suggests the installed toolchain.