Using older Ubuntu image for the basetool release (#467)

# 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

This change steps back the building image of Ubtuntu for basetool binary
releases, so that the users do not have to all update their working
environments.

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

This was tested on 20.04 based docker container image.

## Integration Instructions

N/A

.github/workflows/release-basetools.yml

@@ -39,12 +39,12 @@ jobs:
             output_dir: "BaseTools\\Bin\\Win64"
             target: AARCH64
 
-          - os: ubuntu-22.04
+          - os: ubuntu-20.04
             tool_chain: GCC5
             output_dir: "BaseTools/Source/C/bin"
             target: X64
 
-          - os: ubuntu-22.04
+          - os: ubuntu-20.04
             tool_chain: GCC5
             output_dir: "BaseTools/Source/C/bin"
             target: AARCH64