workflows: make Linux EngFlow builds mandatory

We only delete the Linux ARM64 TeamCity build script because the others
are still necessary for `acceptance` and local roachtest. When those
builds are productionized on GitHub Actions, we can delete the other
Linux build scripts as well.

Epic: CRDB-8308
Release note: None

.github/bors.toml

@@ -7,6 +7,9 @@ status = [
        "check_generated_code",
        "docker_image_amd64",
        "examples_orms",
+       "linux_amd64_build",
+       "linux_amd64_fips_build",
+       "linux_arm64_build",
        "macos_amd64_build",
        "macos_arm64_build",
        "windows_build",

.github/workflows/github-actions-essential-ci.yml

@@ -163,7 +163,7 @@ jobs:
       - name: clean up
         run: ./build/github/cleanup-engflow-keys.sh
         if: always()
-  EXPERIMENTAL_linux_amd64_build:
+  linux_amd64_build:
     runs-on: [self-hosted, basic_runner_group]
     steps:
       - uses: actions/checkout@v4
@@ -181,7 +181,7 @@ jobs:
       - name: clean up
         run: ./build/github/cleanup-engflow-keys.sh
         if: always()
-  EXPERIMENTAL_linux_amd64_fips_build:
+  linux_amd64_fips_build:
     runs-on: [self-hosted, basic_runner_group]
     steps:
       - uses: actions/checkout@v4
@@ -199,7 +199,7 @@ jobs:
       - name: clean up
         run: ./build/github/cleanup-engflow-keys.sh
         if: always()
-  EXPERIMENTAL_linux_arm64_build:
+  linux_arm64_build:
     runs-on: [self-hosted, basic_runner_group]
     steps:
       - uses: actions/checkout@v4