Bump govuk frontend toolkit to 4.6.0
Bump govuk frontend toolkit to 4.6.0

# 4.6.0

- Add breadcrumb styles, separator images and documentation (PR #236)
- Add fallback image for the back link (PR #235)

# 4.5.0

- Find and auto-start JavaScript modules from markup:
`data-module="module-name"`(PR #227)

# 4.4.0

- Add helpers partial for functions
- Add px to em function and documentation

# 4.3.0

- Allow javascript error tracking to be filtered to avoid noise from
plugins

DilwoarH/GDS-Prototype-DM-SavedSearch,alphagov/govuk_prototype_kit,arminio/govuk_prototype_kit,abbott567/govuk_prototype_kit,dwpdigitaltech/hrt-prototype,DilwoarH/GDS-Prototype-DM-SavedSearch,LandRegistry/dmp-prototype,dwpdigitaltech/ejs-prototype,glancyea/tagtest,Demwunz/esif-prototype,alphagov/govuk_prototype_kit,dwpdigitaltech/ejs-prototype,davedark/proto-timeline,LandRegistry/dmp-prototype,Demwunz/esif-prototype,arminio/govuk_prototype_kit,companieshouse/ch-accounts-prototype,LandRegistry/dmp-prototype,dwpdigitaltech/digital-debt,alphagov/govuk_prototype_kit,DilwoarH/GDS-Prototype-DM-SavedSearch,kenmaddison-scc/verify-local-patterns,joelanman/govuk_prototype_kit,gup-dwp/pip-prototype-v2,nhsbsa/ppc-prototype,tsmorgan/marx,davedark/proto-timeline,quis/notify-public-research-prototype,chrishanes/pvb_prisoner_proto,kenmaddison-scc/verify-local-patterns,OrcaTom/dwp_contentpatterns,paulpod/invgov,dwpdigitaltech/digital-debt,gavinwye/govuk_prototype_kit,glancyea/tagtest,arminio/govuk_prototype_kit,danblundell/verify-local-patterns,joelanman/govuk_prototype_kit,dwpdigitaltech/hrt-prototype,samwake/hoddat-cofc-caseworking,davedark/proto-timeline,hannalaakso/accessible-timeout-warning,nhsbsa/ppc-prototype,danblundell/verify-local-patterns,BucksCountyCouncil/verify-local-patterns,paulpod/invgov,paulpod/invgov,glancyea/tagtest,OrcaTom/dwp_contentpatterns,quis/notify-public-research-prototype,samwake/hoddat-cofc-caseworking,chrishanes/pvb_prisoner_proto,BucksCountyCouncil/verify-local-patterns,benjeffreys/hmcts-idam-proto,quis/notify-public-research-prototype,danblundell/verify-local-patterns,abbott567/govuk_prototype_kit,hannalaakso/accessible-timeout-warning,karlparton/my-govuk,companieshouse/ch-accounts-prototype,tsmorgan/marx,samwake/hoddat-cofc-caseworking,joelanman/govuk_prototype_kit,hannalaakso/accessible-timeout-warning,tsmorgan/marx,dwpdigitaltech/digital-debt,karlparton/my-govuk,benjeffreys/hmcts-idam-proto,chrishanes/pvb_prisoner_proto,dwpdigitaltech/hrt-prototype,benjeffreys/hmcts-idam-proto,gup-dwp/pip-prototype-v2,Demwunz/esif-prototype,karlparton/my-govuk,OrcaTom/dwp_contentpatterns,kenmaddison-scc/verify-local-patterns,dwpdigitaltech/ejs-prototype,abbott567/govuk_prototype_kit,nhsbsa/ppc-prototype,BucksCountyCouncil/verify-local-patterns,gavinwye/govuk_prototype_kit,gup-dwp/pip-prototype-v2