ci: Remove cargo symlink workaround

Symlinking $CARGO_HOME to /usr/local/bin made rustup uninstaller delete
the entire folder, causing mysterious build errors, so let's do the
traditional .cargo/env sourcing to make rustup available to the rest of
the build scripts.

Also make sure that required scripts run the shell's rcfile to be able
to setup the PATH correctly.

Signed-off-by: Guilherme Gallo <guilherme.gallo@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33519>

.gitlab-ci/container/container_pre_build.sh

@@ -42,3 +42,10 @@ echo -e "retry_connrefused = on\n" \
 	"retry_on_host_error = on\n" \
 	"retry_on_http_error = 429,500,502,503,504\n" \
         "wait_retry = 32" >> /etc/wgetrc
+
+# Ensure that rust tools are in PATH if they exist
+CARGO_ENV_FILE="$HOME/.cargo/env"
+if [ -f "$CARGO_ENV_FILE" ]; then
+    # shellcheck disable=SC1090
+    source "$CARGO_ENV_FILE"
+fi