Earlier quoted context omitted.
Similarly, a grave accent is sometimes used in poetry to indicate that a single vowel is voiced - e.g. in "cursèd" to indicate that the word should be pronounced as two syllables "curse-ed", rather than a single syllable "curst". Loanwords often retain their accents as well: cliché, façade, doppelgänger, jalapeño.
The adjective "learnèd" (meaning "well-educated") is a native English word that should take the grave accent even outside of poetry. Also "unlearnèd".
Interestingly, as an addition to the parent comment, there's a certain point in time where a lot of -ed words are often spelt -'d, which presumably is from the transitionary period between the expectation that the -ed was pronounced and today's general pronunciation.