Manually standardize quotes where black cannot

Black standardizes single to double quotes where feasible.
However, it doesn't seem to change double to single quotes nor adds
escape characters, as a consequence it skips standardization on
strings with mixed quotes.

Unfortunately, pylint's quote consistency check also doesn't detect
this, so the onus will remain on the reviewer in these cases.

**Unrelated changes**:
The commit still enables pylint's "check-quote-consistency" just in
case it can detect something the black doesn't.

The commit also fixes a syntax inconsistency in pylintrc.

Signed-off-by: Lukas Puehringer <lukas.puehringer@nyu.edu>

tuf/api/metadata.py

@@ -266,12 +266,12 @@ def verify(
         )
 
         if not signatures_for_keyid:
-            raise tuf.exceptions.Error(f'no signature for key {key["keyid"]}.')
+            raise tuf.exceptions.Error(f"no signature for key {key['keyid']}.")
 
         if len(signatures_for_keyid) > 1:
             raise tuf.exceptions.Error(
                 f"{len(signatures_for_keyid)} signatures for key "
-                f'{key["keyid"]}, not sure which one to verify.'
+                f"{key['keyid']}, not sure which one to verify."
             )
 
         if signed_serializer is None:

tuf/api/pylintrc

@@ -44,7 +44,10 @@ max-line-length=80
 single-line-if-stmt=yes
 
 [LOGGING]
-logging-format-style: new
+logging-format-style=new
 
 [MISCELLANEOUS]
 notes=TODO
+
+[STRING]
+check-quote-consistency=yes