Update minimum go version to 1.26.1, golangci-lint to 2.11.2, fix test style (#36876)

Hey, I bumped Go to 1.26.1 and fixed a couple of things I ran into while
poking around.

### Changes

- Bump go.mod from 1.26.0 to 1.26.1 (security patch)
- Bump golangci-lint from v2.10.1 to v2.11.2
- Run make tidy, fmt, lint-go

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.6) <noreply@anthropic.com>

tests/integration/api_repo_get_contents_test.go

@@ -60,7 +60,7 @@ func TestAPIGetContents(t *testing.T) {
 	})
 }
 
-func testAPIGetContents(t *testing.T, u *url.URL) {
+func testAPIGetContents(t *testing.T, _ *url.URL) {
 	/*** SETUP ***/
 	user2 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})         // owner of the repo1 & repo16
 	org3 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 3})          // owner of the repo3, is an org