Enable more revive linter rules (#30608)

Noteable additions:

- `redefines-builtin-id` forbid variable names that shadow go builtins
- `empty-lines` remove unnecessary empty lines that `gofumpt` does not
remove for some reason
- `superfluous-else` eliminate more superfluous `else` branches

Rules are also sorted alphabetically and I cleaned up various parts of
`.golangci.yml`.

modules/markup/markdown/markdown_test.go

@@ -466,7 +466,6 @@ func TestColorPreview(t *testing.T) {
 		res, err := markdown.RenderString(&markup.RenderContext{Ctx: git.DefaultContext}, test.testcase)
 		assert.NoError(t, err, "Unexpected error in testcase: %q", test.testcase)
 		assert.Equal(t, template.HTML(test.expected), res, "Unexpected result in testcase %q", test.testcase)
-
 	}
 
 	negativeTests := []string{
@@ -549,7 +548,6 @@ func TestMathBlock(t *testing.T) {
 		res, err := markdown.RenderString(&markup.RenderContext{Ctx: git.DefaultContext}, test.testcase)
 		assert.NoError(t, err, "Unexpected error in testcase: %q", test.testcase)
 		assert.Equal(t, template.HTML(test.expected), res, "Unexpected result in testcase %q", test.testcase)
-
 	}
 }