Use golangci-lint fmt to format code (#163)

Use `golangci-lint fmt` to format code, upgrading `.golangci.yml` to v2 and mirroring the linter configuration used by https://github.com/go-gitea/gitea. `gci` now handles import ordering into standard, project-local, blank, and default groups.

Mirrors https://github.com/go-gitea/gitea/pull/37194.

Changes:
- Upgrade `.golangci.yml` to v2 format with the same linter set as gitea (minus `prealloc`, `unparam`, `testifylint`, `nilnil` which produced too many pre-existing issues)
- Add path-based exclusions (`bodyclose`, `gosec` in tests; `gosec:G115`/`G117` globally)
- Run lint via `make lint-go` in CI instead of `golangci/golangci-lint-action`, matching the pattern used by other Gitea repos
- Apply safe auto-fixes (`modernize`, `perfsprint`, `usetesting`, etc.)
- Add explanations to existing `//nolint` directives
- Remove dead code (unused `newRemoteReusableWorkflow` and `networkName`), duplicate imports, and shadowed `max` builtins
- Replace deprecated `docker/distribution/reference` with `distribution/reference`
- Fix `Deprecated:` comment casing and simplify nil/len checks

---
This PR was written with the help of Claude Opus 4.7

Reviewed-on: https://gitea.com/gitea/act/pulls/163
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

pkg/runner/action_composite.go

@@ -2,8 +2,9 @@ package runner
 
 import (
 	"context"
-	"fmt"
+	"errors"
 	"regexp"
+	"strconv"
 	"strings"
 
 	"github.com/nektos/act/pkg/common"
@@ -25,7 +26,7 @@ func evaluateCompositeInputAndEnv(ctx context.Context, parent *RunContext, step
 
 	for inputID, input := range step.getActionModel().Inputs {
 		envKey := regexp.MustCompile("[^A-Z0-9-]").ReplaceAllString(strings.ToUpper(inputID), "_")
-		envKey = fmt.Sprintf("INPUT_%s", strings.ToUpper(envKey))
+		envKey = "INPUT_" + strings.ToUpper(envKey)
 
 		// lookup if key is defined in the step but the already
 		// evaluated value from the environment
@@ -90,7 +91,7 @@ func execAsComposite(step actionStep) common.Executor {
 		steps := step.getCompositeSteps()
 
 		if steps == nil || steps.main == nil {
-			return fmt.Errorf("missing steps in composite action")
+			return errors.New("missing steps in composite action")
 		}
 
 		ctx = WithCompositeLogger(ctx, &compositeRC.Masks)
@@ -138,7 +139,7 @@ func (rc *RunContext) compositeExecutor(action *model.Action) *compositeSteps {
 
 	for i, step := range action.Runs.Steps {
 		if step.ID == "" {
-			step.ID = fmt.Sprintf("%d", i)
+			step.ID = strconv.Itoa(i)
 		}
 		step.Number = i