Bump Rust version

[caugner]

Dependency updates are starting to require a later version that we use:

• build(deps): bump url from 2.5.2 to 2.5.7 #672
• build(deps): bump validator from 0.18.1 to 0.20.0 #670

See: https://github.com/mdn/rumba/actions/runs/18861601225/job/53820868540?pr=672#step:8:44

error: rustc 1.81.0 is not supported by the following packages:
  icu_collections@2.0.0 requires rustc 1.82
  icu_collections@2.0.0 requires rustc 1.82
  icu_locale_core@2.0.0 requires rustc 1.82
  icu_locale_core@2.0.0 requires rustc 1.82
  icu_normalizer@2.0.0 requires rustc 1.82
  icu_normalizer@2.0.0 requires rustc 1.82
  icu_normalizer_data@2.0.0 requires rustc 1.82
  icu_normalizer_data@2.0.0 requires rustc 1.82
  icu_normalizer_data@2.0.0 requires rustc 1.82
  icu_normalizer_data@2.0.0 requires rustc 1.82
  icu_properties@2.0.1 requires rustc 1.82
  icu_properties@2.0.1 requires rustc 1.82
  icu_properties_data@2.0.1 requires rustc 1.82
  icu_properties_data@2.0.1 requires rustc 1.82
  icu_properties_data@2.0.1 requires rustc 1.82
  icu_properties_data@2.0.1 requires rustc 1.82
  icu_provider@2.0.0 requires rustc 1.82
  icu_provider@2.0.0 requires rustc 1.82
  idna_adapter@1.2.1 requires rustc 1.82
  idna_adapter@1.2.1 requires rustc 1.82
  litemap@0.8.0 requires rustc 1.82
  litemap@0.8.0 requires rustc 1.82
  potential_utf@0.1.3 requires rustc 1.82
  potential_utf@0.1.3 requires rustc 1.82
  zerotrie@0.2.2 requires rustc 1.82
  zerotrie@0.2.2 requires rustc 1.82
  zerovec@0.11.4 requires rustc 1.82
  zerovec@0.11.4 requires rustc 1.82
Either upgrade rustc or select compatible dependency versions with
`cargo update <name>@<current-ver> --precise <compatible-ver>`
where `<compatible-ver>` is the latest version supporting rustc 1.81.0