GHA: Set a timeout on tests

.github/workflows/linux-interop.yml

@@ -78,6 +78,7 @@ jobs:
                 ../configure --srcdir=`dirname "$PWD"` --enable-maintainer-mode --enable-developer --with-ldap $CONFIGURE_OPTS --prefix=$HOME/inst CFLAGS="${{ matrix.cflags }} -Wno-error=shadow -Wno-error=bad-function-cast -Wno-error=unused-function -Wno-error=unused-result -Wno-error=deprecated-declarations" --with-mitkrb5=$HOME/mitkrb5 --with-older-heimdal=$HOME/oh5l
                 make -j4
             - name: Test
+              timeout-minutes: 20
               env:
                 CC: ${{ matrix.compiler }}
                 MAKEVARS: ${{ matrix.makevars }}