Upgrade golangci-lint from v1 to v2

- Update GOLANGCI_LINT_VERSION from v1.64.8 to v2.0.2
- Migrate .golangci.yml to v2 format:
  - Add version: "2" declaration
  - Move linters-settings under linters.settings

Tracking: redhat-best-practices-for-k8s/telco-bot#49

Author: sebrandon1

.golangci.yml

@@ -1,18 +1,32 @@
+version: "2"
 linters:
-  # disable-all: true
-  # enable-all: true
-  disable:
-    - megacheck
   enable:
-    # megacheck fails to respect build flags, causing compilation failure during linting.
-    # instead, use the unused, gosimple, and staticcheck linters directly
-    - gosimple
     - staticcheck
     - unused
-linters-settings:
-  errcheck:
-    exclude: .errcheck_excludes.txt
-  govet:
-    # disable for those few tests calling t.Fatal from withing go routine.
-    disable:
-      - testinggoroutine
+  settings:
+    errcheck:
+      # Exclude functions from error checking
+      exclude-functions:
+        - (github.com/go-kit/log.Logger).Log
+        - (net.Listener).Close
+        - (*net/http.Response).Body.Close
+        - (io.Closer).Close
+        - io.Closer.Close
+        - fmt.Fprintln
+        - fmt.Fprintf
+    govet:
+      # Disable testinggoroutine for tests calling t.Fatal from goroutines
+      disable:
+        - testinggoroutine
+    staticcheck:
+      # Disable checks that were not enforced in v1 configuration
+      checks:
+        - all
+        - "-SA2002"  # t.Fatal in goroutine (same as govet's testinggoroutine)
+        - "-SA1019"  # deprecated APIs (existing code, not introduced by this PR)
+        - "-SA4006"  # unused value assignments (will fix separately)
+        - "-SA4001"  # *&x simplification
+        - "-ST1000"  # package comments
+        - "-ST1005"  # error string capitalization
+        - "-ST1020"  # function comment format
+        - "-QF1002"  # tagged switch suggestion

Makefile

@@ -13,7 +13,7 @@ LIB_DIR?=./_output/lib
 CACHE_DIR?=$(shell pwd)/_output/cache
 METRICS_JSON=./_output/metrics.json
 GOLANGCI_LINT_BIN=$(BIN_DIR)/golangci-lint
-GOLANGCI_LINT_VERSION=v1.64.8
+GOLANGCI_LINT_VERSION=v2.0.2
 THANOS_BIN=$(BIN_DIR)/thanos
 OTELCOL_BIN=$(BIN_DIR)/otelcol
 PROMETHEUS_BIN=$(BIN_DIR)/prometheus

pkg/runutil/runutil_test.go

@@ -13,14 +13,6 @@ import (
 	"github.com/pkg/errors"
 )
 
-type testCloser struct {
-	err error
-}
-
-func (c testCloser) Close() error {
-	return c.err
-}
-
 type loggerCapturer struct {
 	// WasCalled is true if the Log() function has been called.
 	WasCalled bool