Avoid duplicate definition of --enable-assertions=yes configure flag on Unix builds

- This configuration flag was introduced in commit d47185d in the
  context of PR #3207.
- Moved to the configure step's 'run' command in order to be shared
  across configurations.
- For the sake of reference, matrix.platform.configure should be used
  for configuration flags that are needed for a specific
  platform/architecture (which was the reason it was introduced in
  commit d9255d8, PR #3144).

Author: eduar-hte

.github/workflows/ci.yml

@@ -12,8 +12,8 @@ jobs:
       matrix:
         os: [ubuntu-22.04]
         platform:
-          - {label: "x64", arch: "amd64", configure: "--enable-assertions=yes"}
-          - {label: "x32", arch: "i386", configure: "PKG_CONFIG_PATH=/usr/lib/i386-linux-gnu/pkgconfig CFLAGS=-m32 CXXFLAGS=-m32 LDFLAGS=-m32 --enable-assertions=yes"}
+          - {label: "x64", arch: "amd64", configure: ""}
+          - {label: "x32", arch: "i386", configure: "PKG_CONFIG_PATH=/usr/lib/i386-linux-gnu/pkgconfig CFLAGS=-m32 CXXFLAGS=-m32 LDFLAGS=-m32"}
         compiler:
           - {label: "gcc", cc: "gcc", cxx: "g++"}
           - {label: "clang", cc: "clang", cxx: "clang++"}
@@ -66,7 +66,7 @@ jobs:
         env:
           CC: ${{ matrix.compiler.cc }}
           CXX: ${{ matrix.compiler.cxx }}
-        run: ./configure ${{ matrix.platform.configure }} ${{ matrix.configure.opt }}
+        run: ./configure ${{ matrix.platform.configure }} ${{ matrix.configure.opt }} --enable-assertions=yes
       - uses: ammaraskar/gcc-problem-matcher@master
       - name: make
         run: make -j `nproc`