fix: use temp directory in creds tests to prevent auth.json pollution (knative#3311)

* fix: use temp directory in creds tests to prevent auth.json pollution
Fixes knative#3158
When HOME is empty during tests, testConfigPath now falls back to
t.TempDir() instead of returning an empty string. This prevents
auth.json from being created in the pkg/creds/ directory.

* chore: trigger CI re-run

* chore: remove auth.json from .gitignore

Since the test now uses a temp directory, auth.json is no longer
created in pkg/creds/, so we don't need to ignore it anymore.

Author: Kunal1522

.gitignore

@@ -45,7 +45,3 @@ __pycache__
 # TODO: Update this test to be from a temp directory with a hard-coded impl:
 # https://github.com/knative/func/issues/3196
 /pkg/builders/testdata/go-fn-with-private-deps/.s2i
-
-# TODO: update the test which creates this to run in a temp directory:
-# https://github.com/knative/func/issues/3158
-/pkg/creds/auth.json

pkg/creds/credentials_test.go

@@ -1024,12 +1024,13 @@ func testHomeEnvName() string {
 func testConfigPath(t *testing.T) string {
 	t.Helper()
 	home := os.Getenv(testHomeEnvName())
-	var configPath string
-	if home != "" { // if HOME is not set, don't create config dir
-		configPath = filepath.Join(home, ".config", "func")
-		if err := os.MkdirAll(configPath, os.ModePerm); err != nil {
-			t.Fatal(err)
-		}
+	//  using a temp directory to avoid polluting the source tree with auth.json
+	if home == "" {
+		home = t.TempDir()
+	}
+	configPath := filepath.Join(home, ".config", "func")
+	if err := os.MkdirAll(configPath, os.ModePerm); err != nil {
+		t.Fatal(err)
 	}
 	return configPath
 }
@@ -1039,6 +1040,9 @@ func testConfigPath(t *testing.T) string {
 func testConfigPathError(t *testing.T) (string, error) {
 	t.Helper()
 	home := os.Getenv(testHomeEnvName())
+	if home == "" {
+		home = t.TempDir()
+	}
 	configPath := filepath.Join(home, ".config", "func")
 	return configPath, os.MkdirAll(configPath, os.ModePerm)
 }