Most orbital maneuvers are pretty gentle, because if your engines can accelerate you at a significant fraction of a gee, you probably brought too much engine mass.
Early space capsules had very small maneuvering engines, but somewhat more powerful retrorockets used to lower their orbit promptly for reentry. In Mercury's case there were three retrorockets which normally fired in overlapping sequence; the acceleration would be about 0.4g per rocket or less than 1.2g total. I didn't do the math on it, but at a glance I see that Gemini's retrorocket thrust is higher by roughly the same proportion that the spacecraft is heavier, so it should have similar acceleration. Vostok used a liquid bipropellant retrorocket yielding about 0.35g.
Voskhod had a big solid backup retrorocket in addition that would have produced about 2g for 3 seconds or so but I believe it was not used on the two Voskhod.
Soyuz uses its maneuvering thrusters for retroburn, producing a small fraction of a gee.
If we're counting translunar burns, but not atmospheric reentry (because that would be non-propulsive), then I believe the highest g-force would be Apollo 8's TLI. Apollo 8 lacked a lunar module (though it did have a fairly massive ballast in place of it), so it was the lightest translunar Apollo. At the end of its translunar burn, it would have been accelerating at about 1.5g.
The other likely suspect was the Apollo CSM, which has a rather oversized engine, but the maximum acceleration it could achieve is under 0.75g when completely dry.