What was the idiom for something that we take without a doubt?
"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs ______."
English almost always considers context. It's important to refer to the management cycle for software bugs:
"Bug management includes the process of documenting, categorizing, assigning, reproducing, correcting and releasing the corrected code. Proposed changes to software – bugs as well as enhancement requests and even entire releases – are commonly tracked and managed using bug tracking systems or issue tracking systems.
The items added may be called defects, tickets, issues, or, following the agile development paradigm, stories and epics. Categories may be objective, subjective or a combination, such as version number, area of the software, severity and priority, as well as what type of issue it is, such as a feature request or a bug.".
There's a few things at play here. It comes from the procedure for bug reporting.
You believe that they found something, they don't cry wolf.
They would want you to confirm it, you wouldn't want to send the work out or hire another employee without double checking that they are correct.
You need to assign a priority. Just because someone you trust discovers something doesn't mean that you would drop everything and assemble everyone for a meeting.
So, quite simply, you are accepting the report. You are receiving a bug report from the person, and taking it to the next step; without blindly agreeing with them.
"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs as generally accepted."
That means that they are usually correct, you've not seen a prior error.
"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am subscribing to his bugs."
That means that if they say there is a bug you want to hear about it. He is credible.
"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am triaging his bugs."
That means that when they say there is a bug it goes to you. You double check and categorize it.
"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs as genuine."
That does mean that he is always right, but no one would think that he could never be wrong.
"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs as accredited."
That means that the person is highly experienced, they double check their own work, they are particularly familiar with the work; and it would be most unexpected that they could make an error.
It is for you to decide how much you want to stake your career and credibility on their word. There's also the consideration of whether they are the senior person whom assigns you work or whether you are the senior person whom double checks their work.
To give an analogy, do you want to say:
"You would go mountain climbing with them", or "You would go camping with them".
"You would let them pack the parachutes and fly the plane", or "You pack your own parachute, but enjoy jumping with them".
You want to avoid saying that they could never make any mistake and what they say is always of the most highest priority, they are not a religious leader or feared dictator. Even people here with the highest reputation have received downvotes.
I agree with user Jbro, the literal translation of your literal translation: "I am taking his words as a clean coin." is: His word is good as gold. That is an expression, actual gold would be more valuable unless he is a financial advisor or your software is mission critical.
How you say it reflects on both of you.