Fixes: #6286
When a user is using the passphrase provider and unsets the environment
variables that let them interact with the secrets provider, then would
get an error as follows:
```
▶ pulumi up -y -f
error: decrypting secret value: failed to decrypt: incorrect passphrase, please set PULUMI_CONFIG_PASSPHRASE to the correct passphrase
```
We are oging to change this error message to make it more obvious
to a user what the error is and how they need to fix it
```
▶ pulumi up -y -f
error: constructing secrets manager of type "passphrase": unable to find either `PULUMI_CONFIG_PASSPHRASE` nor `PULUMI_CONFIG_PASSPHRASE_FILE` when trying to access the Passphrase Secrets Manager. Please ensure one of these values are set to allow the operation to continue
```
Ideally, we would like to prompt the user for the passphrase at this
point rather than error, but the CLI could be in the middle of an
update operation as the same codepath is used for reading stackreference
values