"az bicep upgrade" intermittently downgrades bicep version

**Bicep version**
v0.31.34

**Describe the bug**
Since upgrading to v0.31.34, running `az bicep upgrade` intermittently downgrades Bicep to v0.30.23. Re-running `az bicep upgrade` will then re-upgrade to v0.31.34, but this behaviour then repeats when the command is run in future.

Tried uninstalling Bicep and getting a clean install, but the issue persists.

**To Reproduce**
- Upgrade to Bicep v0.31.34.
- Run `az bicep upgrade` again (behaviour is intermittent, doesn't seem to happen every time).

*Terminal output from reproducing the issue with a fresh install:*

```
jamieforsythe@Jamies-MacBook-Pro ~ % ls -a ~/.azure/bin/
. ..
jamieforsythe@Jamies-MacBook-Pro ~ % az bicep install
Installing Bicep CLI v0.30.23...
The configuration value of bicep.use_binary_from_path has been set to 'false'.
Successfully installed Bicep CLI to "/Users/jamieforsythe/.azure/bin/bicep".
jamieforsythe@Jamies-MacBook-Pro ~ % az bicep upgrade
Installing Bicep CLI v0.31.34...
Successfully installed Bicep CLI to "/Users/jamieforsythe/.azure/bin/bicep".
jamieforsythe@Jamies-MacBook-Pro ~ % az bicep version
Bicep CLI version 0.31.34 (ec82b47d63)

jamieforsythe@Jamies-MacBook-Pro ~ % az bicep upgrade
Installing Bicep CLI v0.30.23...
Successfully installed Bicep CLI to "/Users/jamieforsythe/.azure/bin/bicep".
jamieforsythe@Jamies-MacBook-Pro ~ % az bicep version
Bicep CLI version 0.30.23 (ec3612efc7)

jamieforsythe@Jamies-MacBook-Pro ~ % az bicep upgrade
Installing Bicep CLI v0.31.34...
Successfully installed Bicep CLI to "/Users/jamieforsythe/.azure/bin/bicep".
```

**Additional context**
Our organisation has CI processes that run this command to keep our Bicep installation up-to-date, so we need to be able to rely on this command actually installing the latest version.