[chore] Use public Linux ARM64 runners (#6320)

Towards open-telemetry/community#2564

Handles
https://github.blog/changelog/2025-01-16-linux-arm64-hosted-runners-now-available-for-free-in-public-repositories-public-preview/

Switches ARM64 runners to the public version.

.github/workflows/ci.yml

@@ -139,7 +139,7 @@ jobs:
             arch: "386"
           - os: ubuntu-latest
             arch: amd64
-          - os: otel-linux-arm64
+          - os: ubuntu-22.04-arm
             arch: arm64
           - os: macos-13
             arch: amd64

README.md

@@ -56,9 +56,9 @@ Currently, this project supports the following environments.
 | Ubuntu   | 1.24       | 386          |
 | Ubuntu   | 1.23       | 386          |
 | Ubuntu   | 1.22       | 386          |
-| Linux    | 1.24       | arm64        |
-| Linux    | 1.23       | arm64        |
-| Linux    | 1.22       | arm64        |
+| Ubuntu   | 1.24       | arm64        |
+| Ubuntu   | 1.23       | arm64        |
+| Ubuntu   | 1.22       | arm64        |
 | macOS 13 | 1.24       | amd64        |
 | macOS 13 | 1.23       | amd64        |
 | macOS 13 | 1.22       | amd64        |