[Darwin AMR64] Fix version parsing for amd64 fallback tarballs

Summary

Some days ago I switched to Apple Silicon. I still work with a lot of legacy Terraform codebases, so I realized the version parsing not being accurate.

Terraform releases started to ship Darwin ARM64 packages with v1.0.2. In the meantime there where a lot of patch releases currently unable to be installed, as tfenv always tries to fetch the Darwin ARM64 versions instead of the AMD64 fallback one.

Notes

This PR straightens the version parsing, letting tfenv fetching AMD64 tarballs for all pre-v1.0.2 releases on Darwin ARM64.

Current behavior

TFENV_DEBUG=1 tfenv install min-required
[DEBUG] Sourcing helpers from /opt/homebrew/Cellar/tfenv/3.0.0/lib/helpers.sh
DEBUG trap set
Helpers sourced successfully
$PATH does not contain '/opt/homebrew/Cellar/tfenv/3.0.0/libexec', prepending and exporting it now
$PATH does not contain '/opt/homebrew/Cellar/tfenv/3.0.0/bin', prepending and exporting it now
Setting TFENV_DIR to /Users/n3ph/Repositories/ops/terraform/ctp-vault/vault/vault-config
tfenv argument is: install
Long argument provided: install
Resulting command-path: /opt/homebrew/Cellar/tfenv/3.0.0/libexec/tfenv-install
Exec: "/opt/homebrew/Cellar/tfenv/3.0.0/libexec/tfenv-install" "min-required"
TFENV_HELPERS is set, not sourcing helpers again
$PATH already contains '/opt/homebrew/Cellar/tfenv/3.0.0/libexec', not adding it again
$PATH already contains '/opt/homebrew/Cellar/tfenv/3.0.0/bin', not adding it again
Resolving version with: tfenv-resolve-version min-required
TFENV_HELPERS is set, not sourcing helpers again
$PATH already contains '/opt/homebrew/Cellar/tfenv/3.0.0/libexec', not adding it again
$PATH already contains '/opt/homebrew/Cellar/tfenv/3.0.0/bin', not adding it again
Version Requested: min-required
Detecting minimum required version...
Determined min-required to be '0.12.31' (/Users/n3ph/Repositories/ops/terraform/ctp-vault/vault/vault-config/versions.tf:2: required_version = 0.12.31)
Minimum required version detected: 0.12.31
Version is explicit: 0.12.31. Regex enforces the version: ^0.12.31$
Processing install for version 0.12.31, using regex ^0.12.31$
TFENV_HELPERS is set, not sourcing helpers again
$PATH already contains '/opt/homebrew/Cellar/tfenv/3.0.0/libexec', not adding it again
$PATH already contains '/opt/homebrew/Cellar/tfenv/3.0.0/bin', not adding it again
TFENV_REMOTE: https://releases.hashicorp.com
Installing Terraform v0.12.31
Setting curl progress bar with "-#"
Downloading release tarball from https://releases.hashicorp.com/terraform/0.12.31/terraform_0.12.31_darwin_arm64.zip
#=#=-  #       #                                                                                                                                                                                                                                               #=O#-     #        #                                                                                                                                                                                                                                           curl: (22) The requested URL returned error: 404

Tarball download failed

tfutils / tfenv