[safe-string] Use `String.init` to build string.
[safe-string] Use `String.init` to build string.

letouzey/coq-wip,Zimmi48/coq,ejgallego/coq,amintimany/coq,gares/coq,Lionel-Rieg/coq,ppedrot/coq,letouzey/coq-wip,Lionel-Rieg/coq,ejgallego/coq,ppedrot/coq,SkySkimmer/coq,ppedrot/coq,Zimmi48/coq,letouzey/coq-wip,Lionel-Rieg/coq,Zimmi48/coq,ppedrot/coq,maximedenes/coq,Ptival/coq,amintimany/coq,Matafou/coq,JasonGross/coq,william-lawvere/coq,Ptival/coq,coq/coq,maximedenes/coq,Matafou/coq,coq/coq,amintimany/coq,ejgallego/coq,maximedenes/coq,silene/coq,silene/coq,letouzey/coq-wip,gares/coq,letouzey/coq-wip,JasonGross/coq,ejgallego/coq,Matafou/coq,maximedenes/coq,ppedrot/coq,SkySkimmer/coq,Zimmi48/coq,coq/coq,william-lawvere/coq,coq/coq,gares/coq,SkySkimmer/coq,JasonGross/coq,silene/coq,Ptival/coq,SkySkimmer/coq,william-lawvere/coq,gares/coq,maximedenes/coq,JasonGross/coq,gares/coq