Fix initialize_adapter_from_env under no_std.

[kpreid]

Connections
Fixes #7917.

This change should be backported to v26.

Description
Without this change, desired_adapter_name is an undeclared variable.

Testing
Tested with cargo check -p wgpu --no-default-features --features webgl --target wasm32-unknown-unknown

Squash or Rebase?
N/A

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.

[kpreid]

This should probably have a changelog entry but it’ll be guaranteed to conflict with #7916 so I'm waiting for that.

[cwfitzgerald]

I can handle the changelog when I backport, no worries.

[cwfitzgerald]

Backported in v26.0.1