## Description
Add exponential backoff retries to all `go install` and `go mod
download` commands across CI workflows and actions.
## Why
Fixes
[coder/internal#1276](https://github.com/coder/internal/issues/1276) -
CI fails when `sum.golang.org` returns 500 errors during Go module
verification. This is an infrastructure-level flake that can't be
controlled.
## Changes
- Created `.github/scripts/retry.sh` - reusable retry helper with
exponential backoff (2s, 4s, 8s delays, max 3 attempts), using
`scripts/lib.sh` helpers
- Wrapped all `go install` and `go mod download` commands with retry in:
- `.github/actions/setup-go/action.yaml`
- `.github/actions/setup-sqlc/action.yaml`
- `.github/actions/setup-go-tools/action.yaml`
- `.github/workflows/ci.yaml`
- `.github/workflows/release.yaml`
- `.github/workflows/security.yaml`
- Added GNU tools setup (bash 4+, GNU getopt, make 4+) for macOS in
`test-go-pg` job, since `retry.sh` uses `lib.sh` which requires these
tools
Kacper Sawicki