feat: update gcc update alternatives to 15

Author: rjaegers

.devcontainer/cpp/Dockerfile

@@ -159,11 +159,11 @@ RUN --mount=type=cache,target=/cache,sharing=locked \
 # Update all tool alternatives to the correct version
 # and patch root's bashrc to include bash-completion
 RUN --mount=type=cache,target=/var/log,sharing=locked \
- update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-14 10 \
-                        --slave /usr/bin/g++ g++ /usr/bin/g++-14 \
-                        --slave /usr/bin/gcov gcov /usr/bin/gcov-14 \
- && update-alternatives --install /usr/bin/cc cc /usr/bin/gcc-14 10 \
-                        --slave /usr/bin/c++ c++ /usr/bin/g++-14 \
+ update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-15 10 \
+                        --slave /usr/bin/g++ g++ /usr/bin/g++-15 \
+                        --slave /usr/bin/gcov gcov /usr/bin/gcov-15 \
+ && update-alternatives --install /usr/bin/cc cc /usr/bin/gcc-15 10 \
+                        --slave /usr/bin/c++ c++ /usr/bin/g++-15 \
  && update-alternatives --install /usr/bin/iwyu iwyu /usr/local/bin/include-what-you-use 10 \
  && update-alternatives --install /usr/bin/mull-runner mull-runner /usr/bin/mull-runner-${CLANG_VERSION} 10 \
                         --slave /usr/bin/mull-reporter mull-reporter /usr/bin/mull-reporter-${CLANG_VERSION} \