Is there an English language edition of the entirety of Lem's "The Star Diaries" in a single volume?

According to ISFDb the answer is no. Note that while ISFDb may not have all e-books or self-published works, it's pretty comprehensive for published English-language SF, certainly for older works like these. Searching Amazon, which will mostly have newer works, especially e-books, doesn't turn up anything missing.

If we look at "The Twelfth Voyage" (Polish "Podróż dwunasta") we see it is only ever listed as published in The Star Diaries, while "Further Reminiscences of Ijon Tichy I" (Polish "I (Profesor Corcoran)") is only published in Memoirs of a Space Traveler.

There are also a number of stories not in either of those collections, for instance "Ostatnia Podroz Ijona Tichego" (1996), translated in English as "Ijon Tichy's Last Journey to Earth" (1999) which appears to only have been published in Altair Issue Four, and "V: (Tragedia pralnicza)" (1963), translated to English as "The Washing-Machine Tragedy" (1981) published only in The New Yorker, November 30, 1981.

The ISFDb list also includes a few stories, such as "Podróż dwudziesta szósta i ostatnia" (1954) (approximate translation: "The Twenty-sixth and Last Voyage") and "Profesor A. Dońda: (Ze wspomnień Ijona Tichego)" (1974) (approximate translation "Professor A. Donda: From the Memoirs of Ijon Tichy") which do not appear to have ever been translated into English.

Although the ISFDb page for original collection of Ijon Tichy stories, Dzienniki gwiazdowe claims it was split into 2 books when published in English translation

The English language version was published in two volumes. The first volume was published as "Star Diaries" and the second one as "Memoirs of a Space Traveller" in the UK and "Memoirs of a Space Traveler" in the US.

the contents of this edition seem to only include the 12th, 13th, 14th and 22nd through 26th Voyages, and a number of unrelated works. (Specifically, none of the stories that show up in Memoirs appear in this edition.) The ISFDb page does mention "The contents were expanded by new stories and cut out some obsolete ones over the course of time." but only 2 distinct Polish editions are described, which may be down to the weakness of ISFDb for non-English works.

Star Diaries + Memoirs appears to be closer to a split of the 1982 collection Dzienniki gwiazdowe: Wydanie rozszerzone even if that edition appeared later. (This edition also includes a number of stories not translated to English.)

So, unfortunately the answer is "no." There is not only no single-volume work including the stories from Star Diaries and Memoirs, there appear to be a number of stories not included in either, some of which have never even been translated into English.