Apply ruff/flake8-implicit-str-concat rule ISC001

- Revert to multiline strings, as before #255 / ac2fee8.
- Guard the multiline strings from black (and now ruff) unfolding
  them back to a single line.

https://docs.astral.sh/ruff/rules/single-line-implicit-string-concatenation/

testing/test_mercurial.py

@@ -115,12 +115,22 @@ def test_version_from_archival(wd: WorkDir) -> None:
     # entrypoints are unordered,
     # cleaning the wd ensure this test won't break randomly
     wd.cwd.joinpath(".hg").rename(wd.cwd / ".nothg")
-    wd.write(".hg_archival.txt", "node: 000000000000\n" "tag: 0.1\n")
+    wd.write(
+        ".hg_archival.txt",
+        """\
+node: 000000000000
+tag: 0.1
+""",
+    )
     assert wd.get_version() == "0.1"
 
     wd.write(
         ".hg_archival.txt",
-        "node: 000000000000\n" "latesttag: 0.1\n" "latesttagdistance: 3\n",
+        """\
+node: 000000000000
+latesttag: 0.1
+latesttagdistance: 3
+""",
     )
 
     assert wd.get_version() == "0.2.dev3+h000000000000"

testing/test_regressions.py

@@ -35,7 +35,10 @@ def test_pkginfo_noscmroot(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> N
 
     tmp_path.joinpath(".git").mkdir()
     p.joinpath("setup.py").write_text(
-        "from setuptools import setup;" 'setup(use_scm_version={"root": ".."})',
+        """\
+from setuptools import setup
+setup(use_scm_version={"root": ".."})
+""",
         encoding="utf-8",
     )