Use Ubuntu version 20.04 to build basetool to keep backwards compatib…

…ility (#331)

# Preface

Please ensure you have read the [contribution
docs](https://github.com/microsoft/mu/blob/master/CONTRIBUTING.md) prior
to submitting the pull request. In particular,
[pull request
guidelines](https://github.com/microsoft/mu/blob/master/CONTRIBUTING.md#pull-request-best-practices).

## Description

The most recent release of base tool is built using ubuntu-latest, which
caused the binaries not functional in ubuntu development environment
older than ubuntu-latest (which is 22.04 for now).

This change will re-release the basetools based on the 20.04 ubuntu to
hold the sake of backwards compatibility.

For each item, place an "x" in between `[` and `]` if true. Example:
`[x]`.
_(you can also check items in the GitHub UI)_

- [x] Impacts functionality?
- **Functionality** - Does the change ultimately impact how firmware
functions?
- Examples: Add a new library, publish a new PPI, update an algorithm,
...
- [ ] Impacts security?
- **Security** - Does the change have a direct security impact on an
application,
    flow, or firmware?
  - Examples: Crypto algorithm change, buffer overflow fix, parameter
    validation improvement, ...
- [ ] Breaking change?
- **Breaking change** - Will anyone consuming this change experience a
break
    in build or boot behavior?
- Examples: Add a new library class, move a module to a different repo,
call
    a function in a new library class in a pre-existing module, ...
- [ ] Includes tests?
  - **Tests** - Does the change include any explicit test code?
  - Examples: Unit tests, integration tests, robot tests, ...
- [ ] Includes documentation?
- **Documentation** - Does the change contain explicit documentation
additions
    outside direct code modifications (and comments)?
- Examples: Update readme file, add feature readme file, link to
documentation
    on an a separate Web page, ...

## How This Was Tested

Verified on WSL running ubuntu 20.04.

## Integration Instructions

N/A

.azurepipelines/BaseTools-Build-For-Publication.yml

@@ -32,7 +32,7 @@ jobs:
   - job: linux_build
     displayName: Linux Build
     pool:
-      vmImage: ubuntu-latest
+      vmImage: ubuntu-20.04
 
     workspace:
       clean: all