Show line number of failed asserts (pgcentralfoundation#2175)

A little quality-of-life improvement: when a unit test fails, the test
runner now shows the line number. For tests with several assertions,
this is quite handy.

Before:
```
Client Error
assertion `left == right` failed
  left: "hello"
 right: "world"
postgres location: lib.rs
rust location: <unknown>
```

After:
```
Client Error
assertion `left == right` failed
  left: "hello"
 right: "world"
postgres location: lib.rs:22
rust location: <unknown>
```
Signed-off-by: Max Englander <[email protected]>

Author: piki

pgrx-tests/src/framework.rs

@@ -150,8 +150,11 @@ pub fn run_test(
                     return Ok(());
                 }
 
-                let pg_location = dberror.file().unwrap_or("<unknown>").to_string();
+                let mut pg_location = dberror.file().unwrap_or("<unknown>").to_string();
                 let rust_location = dberror.where_().unwrap_or("<unknown>").to_string();
+                if let Some(lineno) = dberror.line() {
+                    pg_location += &format!(":{lineno}");
+                }
 
                 (pg_location, rust_location, received_error_message.to_string())
             } else {