ci: include lib required to delocate on alpine

Since some recent alpine version the krb5-libs package is not installed by
default anymore. When building the libpq the package got installed as a
side effect of installing krb5-dev, but, in case libpq build was cached,
the libraries would have been missing when packaging the wheel or
importing psycopg for test.

scripts/build/build_libpq.sh

@@ -40,11 +40,20 @@ case "$(uname)" in
         ;;
 esac
 
+# Install packages required for test and wheels build, regardless of whether
+# we will build the libpq or not.
+case "$ID" in
+    alpine)
+        apk add --no-cache krb5-libs
+        ;;
+esac
+
 if [[ -f "${LIBPQ_BUILD_PREFIX}/lib/libpq.${library_suffix}" ]]; then
     echo "libpq already available: build skipped" >&2
     exit 0
 fi
 
+# Install packages required to build the libpq.
 case "$ID" in
     centos)
         yum update -y