Fix #733 (#734)

diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 8fe94d1..51f6a04 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -67,7 +67,7 @@
   sanitizers:
     if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
     runs-on: ubuntu-22.04
-    
+
     strategy:
       fail-fast: false
       matrix:
@@ -84,7 +84,7 @@
 
       - name: Build
         run: cmake --build build
-        
+
       - name: Test
         run: ctest --test-dir build --no-tests=error
 
@@ -199,15 +199,15 @@
           - os: ubuntu-latest
             compiler: clang
             version: "13"
-            
+
           - os: ubuntu-latest
             compiler: clang
             version: "14"
-            
+
           - os: ubuntu-latest
             compiler: clang
             version: "15"
-            
+
           - os: macOS-10.15
             compiler: xcode
             version: "10.3"
@@ -223,7 +223,7 @@
           - os: macOS-latest
             compiler: xcode
             version: "13.2.1"
-            
+
           - os: macos-12
             compiler: xcode
             version: "14.0.1"
@@ -242,8 +242,16 @@
           # needed for x86 builds.
           sudo dpkg --add-architecture i386
 
+          sudo apt-get update
+
+          # libc6-dbg:i386 is required for running valgrind on x86.
+          sudo apt-get install -y ninja-build valgrind libc6-dbg:i386 wget gpg ca-certificates
+
           # clang-3.7 and earlier are not available in Bionic anymore so we get
           # them from the Xenial repositories instead.
+          sudo gpg --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5
+          sudo gpg --keyserver keyserver.ubuntu.com --recv-keys 3B4FE6ACC0B21F32
+          #sudo sh -c 'wget -q -O - "https://keyserver.ubuntu.com/pks/lookup?search=0x40976EAF437D05B5&fingerprint=on&op=get" | gpg -q --dearmor - | tee "/usr/share/keyrings/dk.gpg" > /dev/null'
           sudo add-apt-repository "deb http://dk.archive.ubuntu.com/ubuntu/ xenial main"
           sudo add-apt-repository "deb http://dk.archive.ubuntu.com/ubuntu/ xenial universe"
 
@@ -253,11 +261,6 @@
             sudo add-apt-repository "deb https://apt.llvm.org/focal/ llvm-toolchain-focal-${{ matrix.version }} main"
           fi
 
-          sudo apt-get update
-
-          # libc6-dbg:i386 is required for running valgrind on x86.
-          sudo apt-get install -y ninja-build valgrind libc6-dbg:i386
-
           if [ "${{ matrix.compiler }}" = "gcc" ]; then
             sudo apt-get install -y g++-${{ matrix.version }} g++-${{ matrix.version }}-multilib
           else
@@ -340,27 +343,27 @@
   ci-icpc:
     if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
     runs-on: ubuntu-latest
-    
+
     strategy:
       fail-fast: false
       matrix:
         configuration: ["Debug", "Release"]
-    
+
     steps:
       - uses: actions/checkout@v2
-      
+
       - name: Install
         run: |
           wget -O - https://apt.repos.intel.com/intel-gpg-keys/GPG-PUB-KEY-INTEL-SW-PRODUCTS.PUB | sudo apt-key add -
           sudo add-apt-repository "deb https://apt.repos.intel.com/oneapi all main"
           sudo apt-get update
           sudo apt-get install -y intel-oneapi-compiler-dpcpp-cpp-and-cpp-classic ninja-build
-          
+
       - name: Generate
         run: |
           . /opt/intel/oneapi/setvars.sh
           cmake -B build -S . -G Ninja -D CMAKE_CXX_COMPILER=icc -D CMAKE_C_COMPILER=icc -D CMAKE_CXX_COMPILER=icpc -D CMAKE_BUILD_TYPE=${{ matrix.configuration }} -D CMAKE_CXX_FLAGS="-w2 -Wcheck -Werror -diag-disable=10441 -D DOCTEST_CONFIG_NO_CONTRADICTING_INLINE"
-        
+
       - name: Build
         run: |
           . /opt/intel/oneapi/setvars.sh