Improve golden file error messages

[adombeck]

UDENG-5195

This changes the error message from:

Error:      	Not equal: 
expected: map[string]string{"button":"Request new login code", "code":"user_code", "content":"https://verification_uri.com", "foo":"bar", "label":"Scan the QR code or access \"https://verification_uri.com\" and use the provided login code", "type":"qrcode", "wait":"true"}
actual  : map[string]string{"button":"Request new login code", "code":"user_code", "content":"https://verification_uri.com", "label":"Scan the QR code or access \"https://verification_uri.com\" and use the provided login code", "type":"qrcode", "wait":"true"}

Diff:
--- Expected
+++ Actual
@@ -1,2 +1,2 @@
-(map[string]string) (len=7) {
+(map[string]string) (len=6) {
  (string) (len=6) "button": (string) (len=22) "Request new login code",
@@ -4,3 +4,2 @@
  (string) (len=7) "content": (string) (len=28) "https://verification_uri.com",
- (string) (len=3) "foo": (string) (len=3) "bar",
  (string) (len=5) "label": (string) (len=89) "Scan the QR code or access \"https://verification_uri.com\" and use the provided login code",
Test:       	TestSelectAuthenticationMode/Successfully_select_device_auth_qr
Messages:   	SelectAuthenticationMode should have returned the expected layout

to

Error:      	Golden file content mismatch

Expected (golden):
--------------------------------------------------
button: Request new login code
code: user_code
content: https://verification_uri.com
label: Scan the QR code or access "https://verification_uri.com" and use the provided login code
type: qrcode
wait: "true"
foo: bar
--------------------------------------------------

Actual: 
--------------------------------------------------
button: Request new login code
code: user_code
content: https://verification_uri.com
label: Scan the QR code or access "https://verification_uri.com" and use the provided login code
type: qrcode
wait: "true"
--------------------------------------------------

Diff:
--- Expected (golden)
+++ Actual
@@ -4,5 +4,4 @@
 label: Scan the QR code or access "https://verification_uri.com" and use the provided login code
 type: qrcode
 wait: "true"
-foo: bar
 
Test:       	TestSelectAuthenticationMode/Successfully_select_device_auth_qr
Messages:   	Golden file: testdata/TestSelectAuthenticationMode/golden/Successfully_select_device_auth_qr

If delta is installed on the system, the diff is also colorized:

[adombeck]

According to ubuntu/authd#583 (comment), there was a discussion before about changing the Ubuntu version used in our GitHub workflows from jammy to noble, and it was decided that we want to stay on jammy for some reason. If that is correct, I'll have to revert 79afbac, and then we won't have the nice output from delta in our test output. I could live with that, but I wonder why we want to stay on jammy.