refactor(locale): fix en_GB postcode patterns

[ST-DDT]

Third and final part of #2390

• #2390

Related to #3235

• #3235

Blocked by #3223 and #3233

• #3223
• #3233

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Fixes the pattern for en_GB using the patterns from the second page of this document (linked in the original issue)

Valid Formats

The following is a list of the valid formats of postcode. An ‘A’ indicates an alphabetic character, an ‘N’ indicates a numeric character.

Format Example

Outcode	Incode	Postcode
AN	NAA	M1_1AA__
ANN	NAA	M60_1NW_
AAN	NAA	CR2_6XH_
AANN	NAA	DN55_1PT
ANA	NAA	W1P_1HQ_
AANA	NAA	EC1A_1BB

(Where _ represents a space)

The following characters are never used in the inward part of the postcode: C I K M O V

Workaround until this is merged:

const zipCode = faker.helpers.fake([
  '{{helpers.fromRegExp("[A-Z]{1,2}[0-9]{1,2} [0-9][ABDEFGHJLNPQRSTUWXYZ]{2}")}}',
  '{{helpers.fromRegExp("[A-Z]{1,2}[0-9][A-Z] [0-9][ABDEFGHJLNPQRSTUWXYZ]{2}")}}',
]);

(can also be used in browser console on our website)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.96%. Comparing base (b9930dc) to head (c0affe5).

Additional details and impacted files

@@                       Coverage Diff                       @@
##           refactor/location/zipCode/fake    #3234   +/-   ##
===============================================================
  Coverage                           99.96%   99.96%           
===============================================================
  Files                                2805     2805           
  Lines                              217143   217143           
  Branches                              969      969           
===============================================================
+ Hits                               217066   217068    +2     
+ Misses                                 77       75    -2     

Files with missing lines	Coverage Δ
src/locales/en_GB/location/postcode_pattern.ts	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes