Fix obsoletion warnings

[StephenWeatherford]

Microsoft Reviewers: Open in CodeFlow

Fixes #14471

[github-actions]

Test this change out locally with the following install scripts (Action run 10778385141)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 10778385141

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 10778385141"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 10778385141

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 10778385141"

[github-actions]

Dotnet Test Results

    72 files   -     36      72 suites   - 36   26m 12s ⏱️ - 8m 5s
11 044 tests  -     20  11 044 ✅  -     20  0 💤 ±0  0 ❌ ±0 
25 864 runs   - 12 928  25 864 ✅  - 12 928  0 💤 ±0  0 ❌ ±0 

Results for commit 8b30165. ± Comparison against base commit 1a37e89.

♻️ This comment has been updated with latest results.