CI(): fix build caching

[ShaMan123]

Motivation

closes #9403

Description

The build caching was producing a cache for the push to master event.
That is not desired because each time the build changes.
The cache key was wrong (npm-). It was generic so the stale cache was used for a long time.

Changes

Cache the build only for PRs

Gist

In Action

[github-actions]

Build Stats

file / KB (diff)	bundled	minified
fabric	913.552 (0)	305.724 (0)

[github-actions]

Coverage after merging ci-fix-build-caching into master will be

82.92%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
index.node.ts	7.69%	100%	0%	14.29%	17, 20, 23, 35, 38, 41
src
ClassRegistry.ts	100%	100%	100%	100%
Collection.ts	94.71%	94.64%	86.67%	97.09%	101, 104, 207–208, 233–234
CommonMethods.ts	96.55%	87.50%	100%	100%	9
Intersection.ts	100%	100%	100%	100%
Observable.ts	87.76%	85.29%	87.50%	89.58%	134–135, 160–161, 32–33, 41, 50, 78, 89
Point.ts	100%	100%	100%	100%
Shadow.ts	98.36%	95.65%	100%	100%	178
cache.ts	97.06%	90%	100%	100%	57
config.ts	75%	66.67%	66.67%	82.76%	130, 138, 138, 138, 138, 138–140, 151–153
constants.ts	100%	100%	100%	100%
src/Pattern
Pattern.ts	92.31%	91.89%	90%	93.55%	119, 130, 139, 32, 95
src/brushes
BaseBrush.ts	100%	100%	100%	100%
CircleBrush.ts	0%	0%	0%	0%	108, 108, 108, 110, 112, 114–116, 118–121, 128–129, 13, 136, 138, 23–24, 32–36, 40–44, 51–54, 62–66, 68, 76, 76, 76, 76, 76–77, 79, 79, 79–82, 84, 92–93, 95, 97–99
PatternBrush.ts	97.06%	87.50%	100%	100%	21
PencilBrush.ts	91.06%	82.35%	100%	93.81%	122–123, 152, 152–154, 176, 176, 276, 280, 285–286, 68–69, 84–85
SprayBrush.ts	0%	0%	0%	0%	107, 107, 107, 107, 107–108, 110–111, 118–119, 121, 123–127, 136, 140–141, 141, 149, 149, 149–152, 154–157, 161–162, 164, 166–169, 17, 172, 179, 18, 180, 182, 184–185, 187, 194–195, 197–198, 20, 201, 201, 208, 208, 21, 212, 22, 22, 22–24, 28, 32, 39, 46, 53, 60, 67, 84–86, 94–96, 98–99
src/canvas
Canvas.ts	78.99%	77.35%	83.05%	79.61%	1003–1004, 1004, 1004–1006, 1009–1010, 1010, 1010, 1012, 1020, 1020, 1020–1022, 1022, 1022, 1029–1030, 1038–1039, 1039, 1039–1040, 1046, 1048, 1079–1081, 1084–1085, 1089–1090, 1209–1211, 1214–1215, 1288, 1407, 1529, 157, 182, 292–293, 296–300, 305, 328–329, 334–339, 359, 359, 359–360, 360, 360–361, 369, 37, 374–375, 375, 375–376, 378, 387, 393–394, 394, 394, 41, 437, 445, 449, 449, 449–450, 452, 535–536, 536, 536–537, 543, 543, 543–545, 565, 567, 567, 567–568, 568, 568, 571, 571, 571–572, 575, 584–585, 587–588, 590, 590–591, 593–594, 606–607, 607, 607–608, 610–615, 621, 628, 665, 665, 665, 667, 669–674, 680, 686, 686, 686–687, 689, 692, 697, 710, 738, 738, 796–797, 797, 797–798, 800, 803–804, 804, 804–805, 807–808, 811, 811–813, 816–817, 893, 905, 912, 912, 912, 933, 965, 986–987
CanvasOptions.ts	100%	100%	100%	100%
SelectableCanvas.ts	94.35%	92.06%	94.23%	96.20%	1080, 1082, 1084–1085, 301, 471–472, 474–475, 475, 475, 524–525, 586–587, 600, 640–642, 674, 679–680, 707–708, 880, 880–881, 884, 904, 904, 953, 961
StaticCanvas.ts	96.78%	93.09%	100%	98.53%	1031, 1041, 1093–1094, 1097, 1132–1133, 1209, 1218, 1218, 1222, 1222, 1269–1270, 187–188, 204, 571, 583–584, 914–915, 915, 915–916
StaticCanvasOptions.ts	100%	100%	100%	100%
TextEditingManager.ts	84.31%	71.43%	91.67%	88%	17–18, 18, 18–19, 19, 19
src/canvas/DOMManagers
CanvasDOMManager.ts	95.52%	70%	100%	100%	21–22, 29
StaticCanvasDOMManager.ts	97.50%	88.89%	100%	100%	33
util.ts	86.67%	80.56%	83.33%	93.94%	14, 26, 63–64, 67, 67, 74, 93–94
src/color
Color.ts	94.96%	91.67%	96.30%	96.05%	233, 258–259, 267–268, 48
color_map.ts	100%	100%	100%	100%
constants.ts	100%	100%	100%	100%
util.ts	85.71%	76.92%	100%	89.74%	55–56, 56, 58, 58, 58–59, 61–62, 89
src/controls
Control.ts	94.44%	93.10%	91.67%	96.77%	183, 249, 354
changeWidth.ts	100%	100%	100%	100%
commonControls.ts	100%	100%	100%	100%
controlRendering.ts	81.63%	78%	100%	84.78%	106, 111, 121, 121, 45, 50, 61, 61, 65–72, 81–82
drag.ts	100%	100%	100%	100%
fireEvent.ts	88.89%	75%	100%	100%	13
polyControl.ts	7.25%	0%	0%	13.51%	103, 108, 120, 120, 120, 120, 120, 122–125, 125, 128, 135, 17, 25–29, 29, 29, 29, 29, 29, 29, 29, 50–56, 56, 56, 56, 56, 58, 63–64, 66, 76, 82–84, 84, 86, 89–90, 90, 90, 90, 90, 92, 97
rotate.ts	19.57%	12.50%	50%	21.43%	41, 45, 51, 51, 51–52, 55–57, 59, 59, 59, 59, 59–61, 61, 61–63, 65, 65, 65–67, 67, 67–68, 73, 73, 73–74, 76, 78, 80–81
scale.ts	93.57%	92.94%	100%	93.67%	129–130, 132–134, 148–149, 181–183, 42
scaleSkew.ts	78.79%	64.29%	100%	85.71%	27, 29, 29, 29, 31, 33, 35
skew.ts	91.03%	79.31%	100%	97.67%	131–132, 163–164, 171, 177, 179
util.ts	100%	100%	100%	100%
wrapWithFireEvent.ts	100%	100%	100%	100%

[asturur]

This was supposed to rebuild every commit, so i wonder why with master wasn't good.
The sha of head of pr changes every commit and either changes or not changes when merging to master.
In each case the last build should be correct, no?

[asturur]

oh right the merge event probably doesn't have a github.event.pull_request.head.sha but should have something similar we could have used, to reuse the latest one.