Backport PR #52107 on branch 2.0.x (CI: Correctly set PANDAS_CI on ub…

…untu builds) (#52119)

Backport PR #52107: CI: Correctly set PANDAS_CI on ubuntu builds

Co-authored-by: Matthew Roeschke <10647082+mroeschke@users.noreply.github.com>

.github/workflows/ubuntu.yml

@@ -27,7 +27,6 @@ jobs:
         env_file: [actions-38.yaml, actions-39.yaml, actions-310.yaml, actions-311.yaml]
         pattern: ["not single_cpu", "single_cpu"]
         pyarrow_version: ["8", "9", "10"]
-        pandas_ci: [1]
         include:
           - name: "Downstream Compat"
             env_file: actions-38-downstream_compat.yaml
@@ -74,7 +73,7 @@ jobs:
             test_args: "-W error::DeprecationWarning -W error::FutureWarning"
             # TODO(cython3): Re-enable once next-beta(after beta 1) comes out
             # There are some warnings failing the build with -werror
-            pandas_ci: 0
+            pandas_ci: "0"
         exclude:
           - env_file: actions-38.yaml
             pyarrow_version: "8"
@@ -98,7 +97,7 @@ jobs:
       LC_ALL: ${{ matrix.lc_all || '' }}
       PANDAS_DATA_MANAGER: ${{ matrix.pandas_data_manager || 'block' }}
       PANDAS_COPY_ON_WRITE: ${{ matrix.pandas_copy_on_write || '0' }}
-      PANDAS_CI: ${{ matrix.pandas_ci }}
+      PANDAS_CI: ${{ matrix.pandas_ci || '1' }}
       TEST_ARGS: ${{ matrix.test_args || '' }}
       PYTEST_WORKERS: ${{ contains(matrix.pattern, 'not single_cpu') && 'auto' || '1' }}
       PYTEST_TARGET: ${{ matrix.pytest_target || 'pandas' }}