How to write one new line in Bitbucket markdown?

It's now possible to add a forced line break
with two blank spaces at the end of the line:

line1→→
line2

will be formatted as:

line1
line2

I was facing the same issue in bitbucket, and this worked for me:

line1
##<2 white spaces><enter>
line2

It's possible, as addressed in Issue #7396:

When you do want to insert a <br /> break tag using Markdown, you end a line with two or more spaces, then type return or Enter.