Remove extras from the lowerbounds constraints

This fixes the "Constraints cannot have extras" error observed in the pulp-container's CI (pulp/pulp_container#1441).

The workaround was taken from jazzband/pip-tools#1300 (comment).

[noissue]

templates/github/.github/workflows/scripts/before_install.sh.j2

@@ -62,6 +62,7 @@ fi
 
 if [[ "$TEST" = "lowerbounds" ]]; then
   python3 .ci/scripts/calc_deps_lowerbounds.py > lowerbounds_constraints.txt
+  sed -i 's/\[.*\]//g' lowerbounds_constraints.txt
 fi
 
 if [ -f $POST_BEFORE_INSTALL ]; then