ci: fix shellcheck warnings in workflow inline scripts, re-enable actionlint shellcheck integration

## Background

PR #21127 added actionlint, zizmor, and shellcheck to the lint job. actionlint also runs shellcheck internally on `run:` blocks inside workflow YAML files. The repo's QA workflows have many pre-existing shellcheck warnings, so the integration was disabled in that PR to unblock landing. This issue tracks the follow-up cleanup.

## What to do

1. Fix all `warning`-level shellcheck findings in the workflow inline scripts listed below.
2. Remove the `-shellcheck ''` flag from the `actionlint` step in `.github/workflows/lint.yml` to re-enable inline script checking.

`info` and `style` findings (e.g. SC2086 quoting style, SC2129 redirect grouping) do **not** need to be fixed — they are purely stylistic and would need a separate decision.

## Warning-level findings to fix

These are real bugs that can cause incorrect behavior:

| File | Line | Code | Issue |
|------|------|------|-------|
| `ci-cd-main-branch-docker-images.yml` | 37 | SC2046 | Unquoted `$(...)` in `rm -rf` — can glob/split |
| `ci-cd-main-branch-docker-images.yml` | 37 | SC2115 | Missing `${var:?}` guard on path used in `rm -rf` |
| `ci-cd-main-branch-docker-images.yml` | 55 | SC2155 | `local x=$(cmd)` masks command exit code |
| `ci-cd-main-branch-docker-images.yml` | 113 | SC2046 | Unquoted `$(...)` |
| `ci-cd-main-branch-docker-images.yml` | 148 | SC2089/SC2090 | Quoted string stored in variable then re-expanded — use array |
| `ci-cd-main-branch-docker-images.yml` | 148 | SC1083 | Literal `{` / `}` — likely missing `;` or newline |
| `docker-image-remove.yml` | 33 | SC1083 | Literal `{` / `}` in expression |
| `qa-clean-exit-block-downloading.yml` | 82 | SC2046 | Unquoted `$(...)` |
| `qa-clean-exit-snapshot-downloading.yml` | 95 | SC2046 | Unquoted `$(...)` |
| `qa-constrained-tip-tracking.yml` | 141 | SC2046 | Unquoted `$(...)` |
| `qa-rpc-integration-tests-clients.yml` | 43 | SC2034 | Loop variable `i` assigned but never read |
| `qa-rpc-integration-tests-gnosis.yml` | 153 | SC2046 | Unquoted `$(...)` |
| `qa-rpc-integration-tests-latest.yml` | 233 | SC2046 | Unquoted `$(...)` |
| `qa-rpc-integration-tests-polygon.yml` | 93 | SC2034 | Loop variable `i` assigned but never read |
| `qa-rpc-integration-tests-polygon.yml` | 175 | SC2046 | Unquoted `$(...)` |
| `qa-rpc-integration-tests-remote.yml` | 129 | SC2034 | Loop variable `i` unused |
| `qa-rpc-integration-tests-remote.yml` | 250 | SC2046 | Unquoted `$(...)` |
| `qa-rpc-integration-tests.yml` | 154 | SC2046 | Unquoted `$(...)` |
| `qa-rpc-performance-comparison-tests.yml` | 209 | SC2034 | Loop variable `i` unused |
| `qa-rpc-performance-comparison-tests.yml` | 242 | SC2188 | Redirection without a command |
| `qa-rpc-performance-tests.yml` | 207 | SC2034 | Loop variable `i` unused |
| `qa-snap-download.yml` | 84 | SC2046 | Unquoted `$(...)` |
| `qa-stage-exec.yml` | 107 | SC2046 | Unquoted `$(...)` |
| `qa-sync-from-scratch-minimal-node.yml` | 87 | SC2046 | Unquoted `$(...)` |
| `qa-sync-from-scratch.yml` | 112, 193 | SC2046 | Unquoted `$(...)` |
| `qa-sync-with-externalcl.yml` | 104 | SC2046 | Unquoted `$(...)` |
| `qa-tip-tracking-gnosis.yml` | 144 | SC2046 | Unquoted `$(...)` |
| `qa-tip-tracking.yml` | 144 | SC2046 | Unquoted `$(...)` |
| `qa-txpool-performance-test.yml` | 252, 264 | SC2046 | Unquoted `$(...)` (6 instances) |
| `release.yml` | 226, 257, 387 | SC2046 | Unquoted `$(...)` (7 instances) |
| `test-hive-eest.yml` | 72, 240 | SC2046 | Unquoted `$(...)` (5 instances) |

## Re-enabling

Once fixed, remove the `-shellcheck ''` flag from the `actionlint` step in `.github/workflows/lint.yml`:

```yaml
# Before (disabled):
run: actionlint -shellcheck '' --ignore '"workspace" is not defined in object type'

# After (re-enabled):
run: actionlint --ignore '"workspace" is not defined in object type'
```