Fix existing messages in stderrs

Author: JonathanBrouwer

tests/ui/layout/valid_range_oob.stderr

@@ -1,6 +1,6 @@
 
 257 > 255
-error: the compiler unexpectedly panicked. this is a bug.
+error: the compiler unexpectedly panicked. This is a bug
 
 query stack during panic:
 #0 [layout_of] computing layout of `Foo`

tests/ui/mir/lint/storage-live.stderr

@@ -13,7 +13,7 @@ LL |             StorageLive(a);
 
 
 aborting due to `-Z treat-err-as-bug=1`
-error: the compiler unexpectedly panicked. this is a bug.
+error: the compiler unexpectedly panicked. This is a bug
 
 query stack during panic:
 end of query stack

tests/ui/panics/default-backtrace-ice.stderr

@@ -13,7 +13,7 @@ stack backtrace:
 (end_short_backtrace)
 (begin_short_backtrace)
 
-error: the compiler unexpectedly panicked. this is a bug.
+error: the compiler unexpectedly panicked. This is a bug
 
 
 

tests/ui/treat-err-as-bug/err.stderr

@@ -5,7 +5,7 @@ LL | pub static C: u32 = 0 - 1;
    |                     ^^^^^ evaluation of `C` failed here
 
 
-error: the compiler unexpectedly panicked. this is a bug.
+error: the compiler unexpectedly panicked. This is a bug
 
 query stack during panic:
 #0 [eval_static_initializer] evaluating initializer of static `C`

tests/ui/treat-err-as-bug/span_delayed_bug.stderr

@@ -5,7 +5,7 @@ LL | fn main() {}
    | ^^^^^^^^^
 
 
-error: the compiler unexpectedly panicked. this is a bug.
+error: the compiler unexpectedly panicked. This is a bug
 
 query stack during panic:
 #0 [trigger_delayed_bug] triggering a delayed bug for testing incremental