Working around Centos 8 failure. (#3030)

* Experiment using -DCMAKE_BUILD_TYPE=Debug for Centos 8.

* Moving comment because the current placement seems to mess up the cmake command.

* Using `echo > VAR_XXX` and `$(cat VAR_XXX)` trick to emulate using variables (actions/starter-workflows#68 (comment)).

.github/workflows/ci.yml

@@ -592,10 +592,21 @@ jobs:
     - name: Install dependencies
       run: python3 -m pip install cmake -r tests/requirements.txt --prefer-binary
 
+    - name: VAR_BUILD_TYPE 7
+      if: matrix.centos == 7
+      run: echo Release > VAR_BUILD_TYPE
+
+    # Using Debug to avoid segfault that appeared around 2021-06-04,
+    # apparently when the gcc version changed from 8.3 to 8.4.
+    - name: VAR_BUILD_TYPE 8
+      if: matrix.centos == 8
+      run: echo Debug > VAR_BUILD_TYPE
+
     - name: Configure
       shell: bash
       run: >
         cmake -S . -B build
+        -DCMAKE_BUILD_TYPE=$(cat VAR_BUILD_TYPE)
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON