[UK][tesco.com] Expiry Date month autofill does not pass field input validation

Affected Versions:

• All latest Firefox versions using force enable (Nightly 86, Beta RC 85.0, Release 84.0.2)

Tested on:

• MacOS 10.15
• Windows 10 x64

Prerequisites:

• browser.search.region UK
• extensions.formautofill.supportedCountries UK
• download latest Firefox Nightly with region locale (switch extensions.formautofill.available to "on" for testing non-Nightly builds)

Steps to Reproduce:

1. Launch Firefox
2. Go to and reach the payment form Tesco.com
3. Using autofill feature, select 1 saved CC entry - observe Bug 1
4. Fill in manually all the fields and submit the form - observe Bug 2

Expected Results:

1. Expiry month autofill format value should pass the field validation
2. Credit Card Save doorhanger should be displayed after form submission

Actual Results:

1. Bug 1: Expiry month autofill format value does not pass field validation
2. Bug 2: The Credit Card Save doorhanger is not displayed after the form was submitted

Notes:

• Severity: S3 severity, the autofilled exp month value should correctly detect the expected format
• Reproducible on Chrome?: No
• Regression-range: reproducible on all latest versions, this site was never tested before, can look for regression-range if need be