Fixing linter issues

.github/workflows/test.yaml

@@ -1,5 +1,5 @@
 name: Test Go
-on: [push, pull_request]
+on: [push]
 jobs:
   test:
     name: Test

.golangci.yml

@@ -1,11 +1,6 @@
 run:
   tests: true
   max-same-issues: 50
-  skip-dirs:
-    - resources
-    - old
-  skip-files:
-    - cmd/protopkg/main.go
 
 output:
   print-issued-lines: false
@@ -19,13 +14,12 @@ linters:
     - unconvert
     - goimports
     - unused
-    - vetshadow
+    - govet
     - nakedret
     - errcheck
     - revive
     - ineffassign
     - goconst
-    - vet
     - unparam
     - gofmt
 
@@ -45,14 +39,19 @@ linters-settings:
       - ifElseChain
   gofmt:
     rewrite-rules:
-    - pattern:     'interface{}'
-      replacement: 'any'
-    - pattern:     'a[b:len(a)]'
-      replacement: 'a[b:]'
+      - pattern: "interface{}"
+        replacement: "any"
+      - pattern: "a[b:len(a)]"
+        replacement: "a[b:]"
 
 issues:
   max-per-linter: 0
   max-same: 0
+  exclude-dirs:
+    - resources
+    - old
+  exclude-files:
+    - cmd/protopkg/main.go
   exclude-use-default: false
   exclude:
     # Captured by errcheck.

reflect.go

@@ -1098,7 +1098,7 @@ func (t *Schema) MarshalJSON() ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	if t.Extras == nil || len(t.Extras) == 0 {
+	if len(t.Extras) == 0 {
 		return b, nil
 	}
 	m, err := json.Marshal(t.Extras)

reflect_test.go

@@ -429,7 +429,7 @@ func TestSchemaGeneration(t *testing.T) {
 		{&MinValue{}, &Reflector{}, "fixtures/schema_with_minimum.json"},
 		{&TestNullable{}, &Reflector{}, "fixtures/nullable.json"},
 		{&GrandfatherType{}, &Reflector{
-			AdditionalFields: func(r reflect.Type) []reflect.StructField {
+			AdditionalFields: func(_ reflect.Type) []reflect.StructField {
 				return []reflect.StructField{
 					{
 						Name:      "Addr",