What you're looking for is actually the opposite of an agogic accent. Specifically, some agogic accents slightly lengthen the measure they're in (this is the third type currently listed on Wikipedia, which states that the accent has "the effect of temporarily slowing down the tempo").
However, there is no such thing in standard (modern) musical notation. The only way to shorten a single measure is to temporarily change the time-signature and/or the tempo.
But, as a composer living in the 21st century, feel free to introduce your own ad-hoc notation. Just be sure to add a note in your score explaining what the notation means.
Alternatively, as noted in another answer, you could use the archaic form of notation that was traditionally used when notating Gregorian chants, since it appears that that's what you're notating.