Make checks more robust

- exclude unmodified lines from the diff context by searching for lines
  which explicitly start with + or -, meaning added/removed lines. This
  will prevent the script to trigger when adding/modifying other
  constants in the vicinity of the ones that we check for!

- as an extra measure search only for modified lines which also contain
  the word "const" inside of them! This will prevent the script to
  trigger when modifying function calls which merely use the value of
  the constants that we check for!

- as more extra measure examine diff only on the runtime/ directory to
  avoid triggering by changes in this script itself or other files which
  may be referencing a constant name, e.g. text documentation.

NOTE: the script can still trigger with a false positive if for example
you modify a definition for a different constant, whose value is an
expression consuming the constants we check for.

For example:

-const CTC_REWARD_PER_BLOCK: Balance = 2 * CTC;
+const CTC_REWARD_PER_BLOCK: Balance = 2 * CTC * EPOCH_DURATION_IN_BLOCKS;

will trigger the script!

Improve by diffing only runtime/

.github/check-for-changes-in-epoch-duration.sh

@@ -20,7 +20,7 @@ check_block_time() {
     from=$1
     to=$2
 
-    if git --no-pager diff "${from}...${to}" | grep 'MILLISECS_PER_BLOCK'; then
+    if git --no-pager diff "${from}...${to}" -- runtime/ | grep 'MILLISECS_PER_BLOCK' | grep const | grep --regexp='^[\+|\-]'; then
         redprint "FAIL: modified line(s) referencing MILLISECS_PER_BLOCK found!"
         redprint "FAIL: Don't change the value of this variable! This will brick the blockchain!"
         exit 1
@@ -34,7 +34,7 @@ check_blocks_for_faster_epoch() {
     from=$1
     to=$2
 
-    if git --no-pager diff "${from}...${to}" | grep 'BLOCKS_FOR_FASTER_EPOCH'; then
+    if git --no-pager diff "${from}...${to}" -- runtime/ | grep 'BLOCKS_FOR_FASTER_EPOCH' | grep const | grep --regexp='^[\+|\-]'; then
         redprint "FAIL: modified line(s) referencing BLOCKS_FOR_FASTER_EPOCH found!"
         redprint "FAIL: Don't change the value of this variable! This will brick Devnet!"
         exit 1
@@ -48,7 +48,7 @@ check_epoch_duration() {
     from=$1
     to=$2
 
-    if git --no-pager diff "${from}...${to}" | grep 'EPOCH_DURATION'; then
+    if git --no-pager diff "${from}...${to}" -- runtime/ | grep 'EPOCH_DURATION' | grep const | grep --regexp='^[\+|\-]'; then
         redprint "FAIL: modified line(s) referencing EPOCH_DURATION found!"
         redprint "FAIL: Don't change the value of this variable! This will brick the blockchain!"
         exit 1
@@ -62,7 +62,7 @@ check_slot_duration() {
     from=$1
     to=$2
 
-    if git --no-pager diff "${from}...${to}" | grep 'SLOT_DURATION'; then
+    if git --no-pager diff "${from}...${to}" -- runtime/ | grep 'SLOT_DURATION' | grep const | grep --regexp='^[\+|\-]'; then
         redprint "FAIL: modified line(s) referencing SLOT_DURATION found!"
         redprint "FAIL: Don't change the value of this variable! This will brick the blockchain!"
         exit 1